485BPOS

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
FORM N-1A
REGISTRATION STATEMENT (No. 033-52577)
		UNDER THE SECURITIES ACT OF 1933	[X]
		Pre-Effective Amendment No. ____	[ ]
		Post-Effective Amendment No. 33	[X]
and
REGISTRATION STATEMENT (No. 811-07139)
		UNDER THE INVESTMENT COMPANY ACT OF 1940	[X]
		Amendment No. 33	[X]
Fidelity Hereford Street Trust
(Exact Name of Registrant as Specified in Charter)
245 Summer Street, Boston, Massachusetts 02210
(Address Of Principal Executive Offices) (Zip Code)
Registrant's Telephone Number: 617-563-7000
Scott C. Goebel, Secretary
245 Summer Street
Boston, Massachusetts 02210
(Name and Address of Agent for Service)
It is proposed that this filing will become effective
	(X)	immediately upon filing pursuant to paragraph (b).
	( )	on ( ) pursuant to paragraph (b) at 5:30 p.m. Eastern Time.
	( )	60 days after filing pursuant to paragraph (a)(1) at 5:30 p.m. Eastern Time.
	( )	on ( ) pursuant to paragraph (a)(1) of Rule 485 at 5:30 p.m. Eastern Time.
	( )	75 days after filing pursuant to paragraph (a)(2) at 5:30 p.m. Eastern Time.
	( )	on ( ) pursuant to paragraph (a)(2) of Rule 485 at 5:30 p.m. Eastern Time.
If appropriate, check the following box:
	( )	this post-effective amendment designates a new effective date for a previously filed post-effective amendment.

EXHIBIT INDEX

Exhibit	Exhibit No.
XBRL Instance Document	EX-101.INS
XBRL Taxonomy Extension Schema Document	EX-101.SCH
XBRL Taxonomy Extension Calculation Linkbase Document	EX-101.CAL
XBRL Taxonomy Extension Definition Linkbase Document	EX-101.DEF
XBRL Taxonomy Extension Labels Linkbase Document	EX-101.LAB
XBRL Taxonomy Extension Presentation Linkbase Document	EX-101.PRE

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all of the requirements for the effectiveness of this Registration Statement pursuant to Rule 485(b) under the Securities Act of 1933 and has duly caused this Post-Effective Amendment No. 33 to the Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Boston, and Commonwealth of Massachusetts, on the 17th day of July 2013.

	Fidelity Hereford Street Trust
	By	/s/Stephanie J. Dorsey
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||		Stephanie J. Dorsey, President

Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed below by the following persons in the capacities and on the dates indicated.

(Signature)		(Title)	(Date)
/s/Stephanie J. Dorsey		President and Treasurer	July 17, 2013
Stephanie J. Dorsey		(Principal Executive Officer)
/s/Christine Reynolds		Chief Financial Officer	July 17, 2013
Christine Reynolds		(Principal Financial Officer)
/s/Abigail P. Johnson		Trustee	July 17, 2013
Abigail P. Johnson
/s/Elizabeth S. Acton	*	Trustee	July 17, 2013
Elizabeth S. Acton
/s/James C. Curvey	*	Trustee	July 17, 2013
James C. Curvey
/s/Albert R. Gamper, Jr.	*	Trustee	July 17, 2013
Albert R. Gamper, Jr.
/s/Robert F. Gartland	*	Trustee	July 17, 2013
Robert F. Gartland
/s/Arthur E. Johnson	*	Trustee	July 17, 2013
Arthur E. Johnson
/s/Michael E. Kenneally	*	Trustee	July 17, 2013
Michael E. Kenneally
/s/James H. Keyes	*	Trustee	July 17, 2013
James H. Keyes
/s/Marie L. Knowles	*	Trustee	July 17, 2013
Marie L. Knowles
/s/Kenneth L. Wolfe	*	Trustee	July 17, 2013
Kenneth L. Wolfe

*	By:	/s/Joseph R. Fleming
		Joseph R. Fleming, pursuant to powers of attorney dated May 1, 2013 and filed herewith.

POWER OF ATTORNEY

We, the undersigned Directors or Trustees, as the case may be, of the following investment companies:

  Fidelity Aberdeen Street Trust Fidelity Advisor Series II Fidelity Advisor Series IV Fidelity Boylston Street Trust Fidelity California Municipal Trust Fidelity California Municipal Trust II Fidelity Central Investment Portfolios II LLC Fidelity Charles Street Trust Fidelity Colchester Street Trust Fidelity Court Street Trust Fidelity Court Street Trust II Fidelity Garrison Street Trust Fidelity Hereford Street Trust Fidelity Income Fund Fidelity Massachusetts Municipal Trust   Fidelity Merrimack Street Trust Fidelity Money Market Trust Fidelity Municipal Trust Fidelity Municipal Trust II Fidelity Newbury Street Trust Fidelity New York Municipal Trust Fidelity New York Municipal Trust II Fidelity Oxford Street Trust Fidelity Phillips Street Trust Fidelity Revere Street Trust Fidelity Salem Street Trust Fidelity School Street Trust Fidelity Union Street Trust Fidelity Union Street Trust II Variable Insurance Products Fund V

in addition to any other Fidelity Fund for which the undersigned individuals serve as Directors or Trustees (collectively, the "Funds"), hereby revoke all previous powers of attorney we have given to sign and otherwise act in our names and behalf in matters involving any investment company for which FMR or an affiliate acts as investment adviser and hereby constitute and appoint Thomas C. Bogle, Joseph R. Fleming, John V. O'Hanlon, Robert W. Helm and Anthony H. Zacharski, each of them singly, our true and lawful attorneys-in-fact, with full power of substitution, and with full power to each of them, to sign for us and in our names in the appropriate capacities, all Registration Statements of the Funds on Form N-1A, or any successors thereto, any and all subsequent Amendments, Pre-Effective Amendments, or Post-Effective Amendments to said Registration Statements or any successors thereto, and any supplements or other instruments in connection therewith, and generally to do all such things in our names and behalf in connection therewith as said attorneys-in-fact deem necessary or appropriate, to comply with the provisions of the Securities Act of 1933 and the Investment Company Act of 1940, and all related requirements of the Securities and Exchange Commission. We hereby ratify and confirm all that said attorneys-in-fact or their substitutes may do or cause to be done by virtue hereof. This power of attorney is effective for all documents filed on or after May 1, 2013.

WITNESS our hands on this first day of May 1, 2013.

/s/James C. Curvey	/s/Michael E. Kenneally
James C. Curvey	Michael E. Kenneally
/s/Albert R. Gamper, Jr.	/s/James H. Keyes
Albert R. Gamper, Jr.	James H. Keyes
/s/Robert F. Gartland	/s/Marie L. Knowles
Robert F. Gartland	Marie L. Knowles
/s/Arthur E. Johnson	/s/Kenneth L. Wolfe
Arthur E. Johnson	Kenneth L. Wolfe

POWER OF ATTORNEY

I, the undersigned Director or Trustee of the following investment companies:

  Fidelity Aberdeen Street Trust Fidelity Advisor Series IV Fidelity Boylston Street Trust Fidelity California Municipal Trust Fidelity California Municipal Trust II Fidelity Central Investment Portfolios II LLC Fidelity Charles Street Trust Fidelity Garrison Street Trust Fidelity Hereford Street Trust Fidelity Income Fund Fidelity Massachusetts Municipal Trust Fidelity Merrimack Street Trust Fidelity Municipal Trust   Fidelity Municipal Trust II Fidelity Newbury Street Trust Fidelity New York Municipal Trust Fidelity New York Municipal Trust II Fidelity Oxford Street Trust Fidelity Phillips Street Trust Fidelity Revere Street Trust Fidelity Salem Street Trust Fidelity School Street Trust Fidelity Union Street Trust Fidelity Union Street Trust II Variable Insurance Products Fund V

in addition to any other Fidelity Fund for which the undersigned serves as Director or Trustee (collectively, the "Funds"), hereby constitute and appoint Thomas C. Bogle, Joseph R. Fleming, John V. O'Hanlon, Robert W. Helm and Anthony H. Zacharski, each of them singly, my true and lawful attorneys-in-fact, with full power of substitution, and with full power to each of them, to sign for me and in my name in the appropriate capacities, all Registration Statements of the Funds on Form N-1A, or any successors thereto, any and all subsequent Amendments, Pre-Effective Amendments, or Post-Effective Amendments to said Registration Statements or any successors thereto, and any supplements or other instruments in connection therewith, and generally to do all such things in my name and behalf in connection therewith as said attorneys-in-fact deem necessary or appropriate, to comply with the provisions of the Securities Act of 1933 and the Investment Company Act of 1940, and all related requirements of the Securities and Exchange Commission. I hereby ratify and confirm all that said attorneys-in-fact or their substitutes may do or cause to be done by virtue hereof. This power of attorney is effective for all documents filed on or after May 1, 2013.

WITNESS my hand on this first day of May 1, 2013.

/s/Elizabeth S. Acton

Elizabeth S. Acton

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

FIDELITY HEREFORD STREET TRUST

Prospectus Date

rr_ProspectusDate

Jun. 29, 2013

Fidelity Government Money Market Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Fund:
Fidelity^®Government Money Market Fund

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The fund seeks as high a level of current income as is consistent with preservation of capital and liquidity.

Expense [Heading]

rr_ExpenseHeading

Fee Table

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder fees
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual fund operating expenses
(expenses that you pay each year as a % of the value of your investment)

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

This example helps compare the cost of investing in the fund with the cost of investing in other mutual funds.

Let's say, hypothetically, that the annual return for shares of the fund is 5% and that your shareholder fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

• Normally investing at least 80% of assets in U.S. Government securities and repurchase agreements for those securities.
• Investing in U.S. Government securities issued by entities that are chartered or sponsored by Congress but whose securities are neither issued nor guaranteed by the U.S. Treasury.
• Potentially entering into reverse repurchase agreements.
• Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, and diversification of investments.

Risk [Heading]

rr_RiskHeading

Principal Investment Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Interest Rate Changes. Interest rate increases can cause the price of a money market security to decrease.
• Issuer-Specific Changes. A decline in the credit quality of an issuer or a provider of credit support or a maturity-shortening structure for a security can cause the price of a money market security to decrease.

An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the fund.

Risk Money Market Fund [Text]

rr_RiskMoneyMarketFund

Although the fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the fund.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year. Past performance is not an indication of future performance.

Visit www.fidelity.com for updated return information.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The information illustrates the changes in the performance of the fund's shares from year to year.

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.fidelity.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

Past performance is not an indication of future performance.

Bar Chart [Heading]

rr_BarChartHeading

Year-by-Year Returns
Calendar Years

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

During the periods shown in the chart:	Returns	Quarter ended
Highest Quarter Return	1.25%	December 31, 2006
Lowest Quarter Return	0.00%	March 31, 2010
Year-to-Date Return	0.00%	March 31, 2013

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Returns
For the periods ended
December 31, 2012

Fidelity Government Money Market Fund | Class: Fidelity Government Money Market Fund

Risk/Return:

rr_RiskReturnAbstract

Shareholder fees (fees paid directly from your investment)

rr_ShareholderFeeOther

none

Management fee

rr_ManagementFeesOverAssets

0.42%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

none

Total annual fund operating expenses

rr_ExpensesOverAssets

0.42%

1 year

rr_ExpenseExampleYear01

43

3 years

rr_ExpenseExampleYear03

135

5 years

rr_ExpenseExampleYear05

235

10 years

rr_ExpenseExampleYear10

$ 530

2003

rr_AnnualReturn2003

0.83%

2004

rr_AnnualReturn2004

1.02%

2005

rr_AnnualReturn2005

2.87%

2006

rr_AnnualReturn2006

4.71%

2007

rr_AnnualReturn2007

4.90%

2008

rr_AnnualReturn2008

2.31%

2009

rr_AnnualReturn2009

0.32%

2010

rr_AnnualReturn2010

0.01%

2011

rr_AnnualReturn2011

0.01%

2012

rr_AnnualReturn2012

0.01%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-Date Return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2013

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

0.00%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter Return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2006

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

1.25%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter Return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Mar. 31, 2010

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

0.00%

Label

rr_AverageAnnualReturnLabel

Fidelity Government Money Market Fund

Past 1 year

rr_AverageAnnualReturnYear01

0.01%

Past 5 years

rr_AverageAnnualReturnYear05

0.53%

Past 10 years

rr_AverageAnnualReturnYear10

1.68%

XML

Fidelity Money Market Fund

Fund Summary

Fund:
Fidelity^®Money Market Fund

Investment Objective

The fund seeks as high a level of current income as is consistent with preservation of capital and liquidity.

Fee Table

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder fees
(fees paid directly from your investment)

Shareholder Fees (USD $)	Fidelity Money Market Fund Class: Fidelity Money Market Fund
Shareholder fees (fees paid directly from your investment)	none

Annual fund operating expenses
(expenses that you pay each year as a % of the value of your investment)

Annual Fund Operating Expenses	Fidelity Money Market Fund Class: Fidelity Money Market Fund
Management fee	0.42%
Distribution and/or Service (12b-1) fees	none
Other expenses	none
Total annual fund operating expenses	0.42%

This example helps compare the cost of investing in the fund with the cost of investing in other mutual funds.

Let's say, hypothetically, that the annual return for shares of the fund is 5% and that your shareholder fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:

Expense Example (USD $)	Fidelity Money Market Fund Class: Fidelity Money Market Fund
1 year	43
3 years	135
5 years	235
10 years	530

Principal Investment Strategies

• Investing in U.S. dollar-denominated money market securities of domestic and foreign issuers and repurchase agreements.
• Potentially entering into reverse repurchase agreements.
• Investing more than 25% of total assets in the financial services industries.
• Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, and diversification of investments.

Principal Investment Risks

• Interest Rate Changes. Interest rate increases can cause the price of a money market security to decrease.
• Foreign Exposure. Entities located in foreign countries can be affected by adverse political, regulatory, market, or economic developments in those countries.
• Financial Services Exposure. Changes in government regulation and interest rates and economic downturns can have a significant negative effect on issuers in the financial services sector, including the price of their securities or their ability to meet their payment obligations.
• Issuer-Specific Changes. A decline in the credit quality of an issuer or a provider of credit support or a maturity-shortening structure for a security can cause the price of a money market security to decrease.

An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the fund.

Performance

The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year. Past performance is not an indication of future performance.

Visit www.fidelity.com for updated return information.

Year-by-Year Returns
Calendar Years

During the periods shown in the chart:	Returns	Quarter ended
Highest Quarter Return	1.28%	September 30, 2007
Lowest Quarter Return	0.00%	March 31, 2011
Year-to-Date Return	0.00%	March 31, 2013

Average Annual Returns
For the periods ended
December 31, 2012

Average Annual Total Returns	Past 1 year	Past 5 years	Past 10 years
Fidelity Money Market Fund Class: Fidelity Money Market Fund	0.01%	0.71%	1.82%

XML

Fidelity Government Money Market Fund

Fund Summary

Fund:
Fidelity^®Government Money Market Fund

Investment Objective

The fund seeks as high a level of current income as is consistent with preservation of capital and liquidity.

Fee Table

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder fees
(fees paid directly from your investment)

Shareholder Fees (USD $)	Fidelity Government Money Market Fund Class: Fidelity Government Money Market Fund
Shareholder fees (fees paid directly from your investment)	none

Annual fund operating expenses
(expenses that you pay each year as a % of the value of your investment)

Annual Fund Operating Expenses	Fidelity Government Money Market Fund Class: Fidelity Government Money Market Fund
Management fee	0.42%
Distribution and/or Service (12b-1) fees	none
Other expenses	none
Total annual fund operating expenses	0.42%

This example helps compare the cost of investing in the fund with the cost of investing in other mutual funds.

Let's say, hypothetically, that the annual return for shares of the fund is 5% and that your shareholder fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:

Expense Example (USD $)	Fidelity Government Money Market Fund Class: Fidelity Government Money Market Fund
1 year	43
3 years	135
5 years	235
10 years	530

Principal Investment Strategies

• Normally investing at least 80% of assets in U.S. Government securities and repurchase agreements for those securities.
• Investing in U.S. Government securities issued by entities that are chartered or sponsored by Congress but whose securities are neither issued nor guaranteed by the U.S. Treasury.
• Potentially entering into reverse repurchase agreements.
• Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, and diversification of investments.

Principal Investment Risks

• Interest Rate Changes. Interest rate increases can cause the price of a money market security to decrease.
• Issuer-Specific Changes. A decline in the credit quality of an issuer or a provider of credit support or a maturity-shortening structure for a security can cause the price of a money market security to decrease.

An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the fund.

Performance

The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year. Past performance is not an indication of future performance.

Visit www.fidelity.com for updated return information.

Year-by-Year Returns
Calendar Years

During the periods shown in the chart:	Returns	Quarter ended
Highest Quarter Return	1.25%	December 31, 2006
Lowest Quarter Return	0.00%	March 31, 2010
Year-to-Date Return	0.00%	March 31, 2013

Average Annual Returns
For the periods ended
December 31, 2012

Average Annual Total Returns	Past 1 year	Past 5 years	Past 10 years
Fidelity Government Money Market Fund Class: Fidelity Government Money Market Fund	0.01%	0.53%	1.68%

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	FIDELITY HEREFORD STREET TRUST
Prospectus Date	rr_ProspectusDate	Jun. 29, 2013
Document Creation Date	dei_DocumentCreationDate	Jun. 27, 2013

XML

Fidelity Treasury Only Money Market Fund

Fund Summary

Fund:
Fidelity^®Treasury Only Money Market Fund

Investment Objective

The fund seeks as high a level of current income as is consistent with the security of principal and liquidity.

Fee Table

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder fees
(fees paid directly from your investment)

Shareholder Fees (USD $)	Fidelity Treasury Only Money Market Fund Class: Fidelity Treasury Only Money Market Fund
Shareholder fees (fees paid directly from your investment)	none

Annual fund operating expenses
(expenses that you pay each year as a % of the value of your investment)

Annual Fund Operating Expenses	Fidelity Treasury Only Money Market Fund Class: Fidelity Treasury Only Money Market Fund
Management fee	0.42%
Distribution and/or Service (12b-1) fees	none
Other expenses	none
Total annual fund operating expenses	0.42%

This example helps compare the cost of investing in the fund with the cost of investing in other mutual funds.

Let's say, hypothetically, that the annual return for shares of the fund is 5% and that your shareholder fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:

Expense Example (USD $)	Fidelity Treasury Only Money Market Fund Class: Fidelity Treasury Only Money Market Fund
1 year	43
3 years	135
5 years	235
10 years	530

Principal Investment Strategies

• Normally investing at least 80% of assets in U.S. Treasury securities.
• Potentially entering into reverse repurchase agreements.
• Normally investing in securities whose interest is exempt from state and local income taxes.
• Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, and diversification of investments.

Principal Investment Risks

• Interest Rate Changes. Interest rate increases can cause the price of a money market security to decrease.
• Issuer-Specific Changes. A decline in the credit quality of an issuer or a provider of credit support or a maturity-shortening structure for a security can cause the price of a money market security to decrease.

An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the fund.

Performance

The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year. Past performance is not an indication of future performance.

Visit www.fidelity.com for updated return information.

Year-by-Year Returns
Calendar Years

During the periods shown in the chart:	Returns	Quarter ended
Highest Quarter Return	1.18%	December 31, 2006
Lowest Quarter Return	0.00%	March 31, 2010
Year-to-Date Return	0.00%	March 31, 2013

Average Annual Returns
For the periods ended
December 31, 2012

Average Annual Total Returns	Past 1 year	Past 5 years	Past 10 years
Fidelity Treasury Only Money Market Fund Class: Fidelity Treasury Only Money Market Fund	0.01%	0.31%	1.46%

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

FIDELITY HEREFORD STREET TRUST

Prospectus Date

rr_ProspectusDate

Jun. 29, 2013

Fidelity Money Market Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Fund:
Fidelity^®Money Market Fund

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The fund seeks as high a level of current income as is consistent with preservation of capital and liquidity.

Expense [Heading]

rr_ExpenseHeading

Fee Table

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder fees
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual fund operating expenses
(expenses that you pay each year as a % of the value of your investment)

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

This example helps compare the cost of investing in the fund with the cost of investing in other mutual funds.

Let's say, hypothetically, that the annual return for shares of the fund is 5% and that your shareholder fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

• Investing in U.S. dollar-denominated money market securities of domestic and foreign issuers and repurchase agreements.
• Potentially entering into reverse repurchase agreements.
• Investing more than 25% of total assets in the financial services industries.
• Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, and diversification of investments.

Strategy Portfolio Concentration [Text]

rr_StrategyPortfolioConcentration

• Investing more than 25% of total assets in the financial services industries.

Risk [Heading]

rr_RiskHeading

Principal Investment Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Interest Rate Changes. Interest rate increases can cause the price of a money market security to decrease.
• Foreign Exposure. Entities located in foreign countries can be affected by adverse political, regulatory, market, or economic developments in those countries.
• Financial Services Exposure. Changes in government regulation and interest rates and economic downturns can have a significant negative effect on issuers in the financial services sector, including the price of their securities or their ability to meet their payment obligations.
• Issuer-Specific Changes. A decline in the credit quality of an issuer or a provider of credit support or a maturity-shortening structure for a security can cause the price of a money market security to decrease.

An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the fund.

Risk Money Market Fund [Text]

rr_RiskMoneyMarketFund

Although the fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the fund.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance

Performance Narrative [Text Block]

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The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year. Past performance is not an indication of future performance.

Visit www.fidelity.com for updated return information.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The information illustrates the changes in the performance of the fund's shares from year to year.

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.fidelity.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

Past performance is not an indication of future performance.

Bar Chart [Heading]

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Year-by-Year Returns
Calendar Years

Bar Chart Closing [Text Block]

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During the periods shown in the chart:	Returns	Quarter ended
Highest Quarter Return	1.28%	September 30, 2007
Lowest Quarter Return	0.00%	March 31, 2011
Year-to-Date Return	0.00%	March 31, 2013

Performance Table Heading

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Average Annual Returns
For the periods ended
December 31, 2012

Fidelity Money Market Fund | Class: Fidelity Money Market Fund

Risk/Return:

rr_RiskReturnAbstract

Shareholder fees (fees paid directly from your investment)

rr_ShareholderFeeOther

none

Management fee

rr_ManagementFeesOverAssets

0.42%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

none

Total annual fund operating expenses

rr_ExpensesOverAssets

0.42%

1 year

rr_ExpenseExampleYear01

43

3 years

rr_ExpenseExampleYear03

135

5 years

rr_ExpenseExampleYear05

235

10 years

rr_ExpenseExampleYear10

$ 530

2003

rr_AnnualReturn2003

0.88%

2004

rr_AnnualReturn2004

1.07%

2005

rr_AnnualReturn2005

2.95%

2006

rr_AnnualReturn2006

4.79%

2007

rr_AnnualReturn2007

5.09%

2008

rr_AnnualReturn2008

2.90%

2009

rr_AnnualReturn2009

0.62%

2010

rr_AnnualReturn2010

0.03%

2011

rr_AnnualReturn2011

0.01%

2012

rr_AnnualReturn2012

0.01%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-Date Return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2013

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

0.00%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter Return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2007

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

1.28%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter Return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Mar. 31, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

0.00%

Label

rr_AverageAnnualReturnLabel

Fidelity Money Market Fund

Past 1 year

rr_AverageAnnualReturnYear01

0.01%

Past 5 years

rr_AverageAnnualReturnYear05

0.71%

Past 10 years

rr_AverageAnnualReturnYear10

1.82%

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

FIDELITY HEREFORD STREET TRUST

Prospectus Date

rr_ProspectusDate

Jun. 29, 2013

Fidelity Treasury Only Money Market Fund

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

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Fund Summary

Fund:
Fidelity^®Treasury Only Money Market Fund

Objective [Heading]

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Investment Objective

Objective, Primary [Text Block]

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The fund seeks as high a level of current income as is consistent with the security of principal and liquidity.

Expense [Heading]

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Fee Table

Expense Narrative [Text Block]

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The following table describes the fees and expenses that may be incurred when you buy and hold shares of the fund.

Shareholder Fees Caption [Text]

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Shareholder fees
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual fund operating expenses
(expenses that you pay each year as a % of the value of your investment)

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

This example helps compare the cost of investing in the fund with the cost of investing in other mutual funds.

Let's say, hypothetically, that the annual return for shares of the fund is 5% and that your shareholder fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:

Strategy [Heading]

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Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

• Normally investing at least 80% of assets in U.S. Treasury securities.
• Potentially entering into reverse repurchase agreements.
• Normally investing in securities whose interest is exempt from state and local income taxes.
• Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, and diversification of investments.

Risk [Heading]

rr_RiskHeading

Principal Investment Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Interest Rate Changes. Interest rate increases can cause the price of a money market security to decrease.
• Issuer-Specific Changes. A decline in the credit quality of an issuer or a provider of credit support or a maturity-shortening structure for a security can cause the price of a money market security to decrease.

An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the fund.

Risk Money Market Fund [Text]

rr_RiskMoneyMarketFund

Although the fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the fund.

Risk Not Insured Depository Institution [Text]

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An investment in the fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

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Performance

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year. Past performance is not an indication of future performance.

Visit www.fidelity.com for updated return information.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The information illustrates the changes in the performance of the fund's shares from year to year.

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.fidelity.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

Past performance is not an indication of future performance.

Bar Chart [Heading]

rr_BarChartHeading

Year-by-Year Returns
Calendar Years

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

During the periods shown in the chart:	Returns	Quarter ended
Highest Quarter Return	1.18%	December 31, 2006
Lowest Quarter Return	0.00%	March 31, 2010
Year-to-Date Return	0.00%	March 31, 2013

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Returns
For the periods ended
December 31, 2012

Fidelity Treasury Only Money Market Fund | Class: Fidelity Treasury Only Money Market Fund

Risk/Return:

rr_RiskReturnAbstract

Shareholder fees (fees paid directly from your investment)

rr_ShareholderFeeOther

none

Management fee

rr_ManagementFeesOverAssets

0.42%

Distribution and/or Service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

none

Total annual fund operating expenses

rr_ExpensesOverAssets

0.42%

1 year

rr_ExpenseExampleYear01

43

3 years

rr_ExpenseExampleYear03

135

5 years

rr_ExpenseExampleYear05

235

10 years

rr_ExpenseExampleYear10

$ 530

2003

rr_AnnualReturn2003

0.75%

2004

rr_AnnualReturn2004

0.92%

2005

rr_AnnualReturn2005

2.64%

2006

rr_AnnualReturn2006

4.42%

2007

rr_AnnualReturn2007

4.38%

2008

rr_AnnualReturn2008

1.49%

2009

rr_AnnualReturn2009

0.05%

2010

rr_AnnualReturn2010

0.01%

2011

rr_AnnualReturn2011

0.01%

2012

rr_AnnualReturn2012

0.01%

Year to Date Return, Label

rr_YearToDateReturnLabel

Year-to-Date Return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Mar. 31, 2013

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

0.00%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarter Return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2006

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

1.18%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarter Return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Mar. 31, 2010

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

0.00%

Label

rr_AverageAnnualReturnLabel

Fidelity Treasury Only Money Market Fund

Past 1 year

rr_AverageAnnualReturnYear01

0.01%

Past 5 years

rr_AverageAnnualReturnYear05

0.31%

Past 10 years

rr_AverageAnnualReturnYear10

1.46%

XML

Document and Entity Information	12 Months Ended
	Jun. 29, 2013
Risk/Return:
Document Type	485BPOS
Document Period End Date	Apr. 30, 2013
Registrant Name	FIDELITY HEREFORD STREET TRUST
Central Index Key	0000917286
Amendment Flag	false
Document Creation Date	Jun. 27, 2013
Document Effective Date	Jun. 29, 2013
Prospectus Date	Jun. 29, 2013