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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2013-03-29</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001501364</issuerCik>
        <issuerName>Rockville Financial, Inc. /CT/</issuerName>
        <issuerTradingSymbol>RCKB</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001452142</rptOwnerCik>
            <rptOwnerName>Lund John T</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>ROCKVILLE FINANCIAL, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>45 GLASTONBURY BOULEVARD</rptOwnerStreet2>
            <rptOwnerCity>GLASTONBURY</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06033</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP/CFO/Treasurer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2013-03-29</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>157</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>12.94</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>25256</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                    <footnoteId id="F6"/>
                    <footnoteId id="F7"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3586.946</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Rockville Bank 401(k) Plan</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7825.4279</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F8"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Rockville Bank ESOP Plan</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Options</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>6.09</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2009-03-16</value>
                <footnoteId id="F9"/>
            </exerciseDate>
            <expirationDate>
                <value>2019-03-16</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>9479</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>9479</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Options</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>7.42</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2010-11-15</value>
                <footnoteId id="F10"/>
            </exerciseDate>
            <expirationDate>
                <value>2020-11-15</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>6976</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6976</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Options</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>9.50</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2011-09-02</value>
                <footnoteId id="F11"/>
            </exerciseDate>
            <expirationDate>
                <value>2021-09-02</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>15689</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>15689</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Options</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>10.99</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2012-06-21</value>
                <footnoteId id="F12"/>
            </exerciseDate>
            <expirationDate>
                <value>2022-06-21</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>19292</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>19292</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Options</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>10.99</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2012-06-21</value>
                <footnoteId id="F13"/>
            </exerciseDate>
            <expirationDate>
                <value>2022-06-21</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>54352</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>54352</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Includes 200 shares held jointly with wife.</footnote>
        <footnote id="F2">Transaction representing shares withheld by the Issuer for tax withholding purposes with respect to the vesting of Restricted Stock previously issued to the Reporting Person by the Issuer under its 2006 Stock Incentive Award Plan.</footnote>
        <footnote id="F3">Includes 1,484 restricted stock granted pursuant to the Rockville Financial, Inc. 2006 Stock Incentive Award Plan.  The original grant of 1,500 shares (x 1.5167 exchange ratio became 2,275 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 791 shares (226 x 1.5167 exchange ratio became 342 shares in March 2011, plus 449 shares since that time) withheld by the Issuer for tax withholding purposes.</footnote>
        <footnote id="F4">Includes 1,811 restricted shares granted pursuant to the Rockville Financial, Inc. 2006 Stock Incentive Award Plan.  The original grant of 1,500 shares (x 1.5167 exchange ratio became 2,275 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 307 shares (77 x 1.5167 exchange ratio became 116 shares in March 2011, plus 348 shares since that time) withheld by the Issuer for tax withholding purposes.</footnote>
        <footnote id="F5">Includes 2,645 restricted shares granted pursuant to the Rockville Financial, Inc. 2006 Stock Incentive Award Plan.  The original grant of 3,094 shares vest in equal 20% increments over a five year period, the first 20% vesting on September 2, 2011 and the subsequent vesting on each annual anniversary of that date.  The reported number of shares is net of 449 shares withheld by the Issuer for tax withholding purposes.</footnote>
        <footnote id="F6">Includes 13,944 restricted shares granted pursuant to the Rockville Financial, Inc.'s 2012 Stock Incentive Plan.  The original grant of 15,212 shares vest in four equal annual installments of 25%, with the first 25% vesting on June 21, 2012 and the subsequent vesting on each annual anniversary of the grant date thereafter.  The reported number of shares is net of 1,268 shares withheld by the Issuer for tax withholding purposes.</footnote>
        <footnote id="F7">Includes 5,071 restricted shares granted pursuant to the Rockville Financial, Inc.'s 2012 Stock Incentive Plan and cliff vest on the third anniversary of the grant date, if, and only if Rockville Financial, Inc. meets certain performance goals.</footnote>
        <footnote id="F8">Shares allocated to the account of Mr. Lund under the Rockville Bank Employee Stock Ownership Plan, of which 4,695.25674 shares are vested.</footnote>
        <footnote id="F9">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="F10">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>
        <footnote id="F11">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 September 2, 2011 and the subsequent vesting on each annual anniversary of that date.</footnote>
        <footnote id="F12">Stock options granted pursuant to the Rockville Financial, Inc.'s 2006 Stock Incentive Award Plan and will become exercisable in five equal annual installments of 20%, the first 20% becoming exercisable on June 21, 2012 and the subsequent vesting on each annual anniversary of the grant date thereafter.</footnote>
        <footnote id="F13">Stock options granted pursuant to the Rockville Financial, Inc.'s 2012 Stock Incentive Plan and will become exercisable in four equal annual installments of 25%, the first 25% becoming exercisable on June 21, 2012 and the subsequent vesting on each annual anniversary of the grant date thereafter.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Marliese L. Shaw by POA</signatureName>
        <signatureDate>2013-04-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
