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

    <schemaVersion>X0305</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-06-21</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 NEW, 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>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP, CFO, Treasurer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2012-06-21</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>15212</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>21979</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                    <footnoteId id="F6"/>
                    <footnoteId id="F5"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F7"/>
            </securityTitle>
            <transactionDate>
                <value>2012-06-21</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5071</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>27050</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2158.0445</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>5901.7949</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>
                <footnoteId id="F9"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>6.09</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2009-03-16</value>
            </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>
                <footnoteId id="F10"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>7.42</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2010-11-15</value>
            </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>
                <footnoteId id="F11"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>9.50</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2011-09-02</value>
            </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>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Options</value>
                <footnoteId id="F12"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>10.99</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2012-06-21</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>19292</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2012-06-21</value>
            </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>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Options</value>
                <footnoteId id="F13"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>10.99</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2012-06-21</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>54352</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2012-06-21</value>
            </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>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Restricted stock granted pursuant to the Rockville Financial, Inc.'s 2012 Stock Incentive Plan and will vest in four equal annual installments of 25%, with the first installment to vest on the grant date and an additional 25% to vest on each annual anniversary of the grant date thereafter.</footnote>
        <footnote id="F2">Includes 200 shares held jointly with wife.</footnote>
        <footnote id="F3">Includes 1,796 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 226 shares (x 1.5167 exchange ratio became 478 shares) withheld by the Issuer for tax withholding purposes.</footnote>
        <footnote id="F4">Includes 2,158 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 77 shares (x 1.5167 exchange ratio became 116 shares) withheld by the Issuer for tax withholding purposes.</footnote>
        <footnote id="F5">Includes 3,094 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 428 shares withheld by the Issuer for tax withholding purposes.</footnote>
        <footnote id="F6">The reported number of shares is net of 156 shares withheld by the Issuer for tax withholding purposes.</footnote>
        <footnote id="F7">Restricted stock 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. meeting 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 2,360.7180 shares are vested as of March 30, 2012.</footnote>
        <footnote id="F9">Stock options granted pursuant to the Rockville Financial, Inc. 2006 Stock Incentive Award Plan and are 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 are 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%, with the first installment to vest on the grant date and an additional 20% to vest 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%, with the first installment to vest on the grant date and an additional 25% to vest on each annual anniversary of the grant date thereafter.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Marliese L. Shaw by POA</signatureName>
        <signatureDate>2012-06-22</signatureDate>
    </ownerSignature>
</ownershipDocument>
