<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>5</documentType>

    <periodOfReport>2010-12-31</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <form3HoldingsReported>0</form3HoldingsReported>

    <form4TransactionsReported>0</form4TransactionsReported>

    <issuer>
        <issuerCik>0001311131</issuerCik>
        <issuerName>Rockville Financial Inc.</issuerName>
        <issuerTradingSymbol>RCKB</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001418108</rptOwnerCik>
            <rptOwnerName>DiChiara Richard C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>ROCKVILLE FINANCIAL, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>1645 ELLINGTON ROAD</rptOwnerStreet2>
            <rptOwnerCity>SOUTH WINDSOR</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06074</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>SVP/Rockville Bank</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionCoding>
                <transactionFormType></transactionFormType>
            </transactionCoding>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2573</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-12-31</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1020.7044</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2844.4255</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Rockville Bank ESOP Plan</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Options</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>11.98</value>
            </conversionOrExercisePrice>
            <transactionCoding>
                <transactionFormType></transactionFormType>
            </transactionCoding>
            <exerciseDate>
                <value>2008-02-20</value>
                <footnoteId id="F6"/>
            </exerciseDate>
            <expirationDate>
                <value>2018-02-20</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1625</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1625</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Options</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>9.24</value>
            </conversionOrExercisePrice>
            <transactionCoding>
                <transactionFormType></transactionFormType>
            </transactionCoding>
            <exerciseDate>
                <value>2009-03-16</value>
                <footnoteId id="F7"/>
            </exerciseDate>
            <expirationDate>
                <value>2019-03-16</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5400</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5400</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Options</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>11.25</value>
            </conversionOrExercisePrice>
            <transactionCoding>
                <transactionFormType></transactionFormType>
            </transactionCoding>
            <exerciseDate>
                <value>2010-11-15</value>
                <footnoteId id="F8"/>
            </exerciseDate>
            <expirationDate>
                <value>2020-11-15</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4335</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4335</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Includes 775 shares of restricted stock granted pursuant to the Rockville Financial, Inc. 2006 Stock Incentive Award Plan. The original grant of 1,000 shares will become exercisable in equal 20% increments over a five year period, the first 20% becoming exercisable on February 20, 2008 and the subsequent vesting on each annual anniversary of that date. The reported number of shares is net of 225 shares withheld by the Issuer for tax withholding purposes.</footnote>
        <footnote id="F2">Includes 850 restricted stock granted pursuant to the Rockville Financial, Inc. 2006 Stock Incentive Award Plan. The original grant of 1,000 shares will become vested in equal 20% increments over a five year period, the first 20% vesting on March 16, 2009 and the subsequent vesting on each annual anniversary of that date. The reported number of shares is net of 150 shares withheld by the Issuer for tax withholding purposes.</footnote>
        <footnote id="F3">Includes 948 restricted shares granted pursuant to the Rockville Financial, Inc. 2006 Stock Incentive Award Plan. The original grant of 1,000 shares vest in equal 20% increments over a five year period, the first 20% vesting on November 15, 2010 and the subsequent vesting on each annual anniversary of that date. The reported number of shares is net of 52 shares withheld by the Issuer for tax withholding purposes.</footnote>
        <footnote id="F4">Shares allocated to the account of Mr. DiChiara under the Rockville Bank Employee Stock Ownership Plan, of which 1,137.7702 shares are vested as of December 31, 2010.</footnote>
        <footnote id="F5">Total beneficial ownership is 5,417.4255 at 12/31/2010.</footnote>
        <footnote id="F6">Stock options granted pursuant to the Rockville Financial, Inc. 2006 Stock Incentive Award Plan and will become exercisable in equal 20% increments over a five year period, the first 20% becoming exercisable on February 20, 2008 and the subsequent vesting on each annual anniversary of that date.</footnote>
        <footnote id="F7">Stock options granted pursuant to the Rockville Financial, Inc. 2006 Stock Incentive Award Plan and will become exercisable in equal 20% increments over a five year period, the first 20% becoming exercisable on March 16, 2009 and the subsequent vesting on each annual anniversary of that date.</footnote>
        <footnote id="F8">Stock options granted pursuant to the Rockville Financial, Inc. 2006 Stock Incentive Award Plan and will become exercisable in equal 20% increments over a five year period, the first 20% becoming exercisable on November 15, 2010 and the subsequent vesting on each annual anniversary of that date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Marliese L. Shaw by POA</signatureName>
        <signatureDate>2011-02-11</signatureDate>
    </ownerSignature>
</ownershipDocument>
