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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-02-22</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001320934</issuerCik>
        <issuerName>International Coal Group, Inc.</issuerName>
        <issuerTradingSymbol>ICO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001435653</rptOwnerCik>
            <rptOwnerName>Beckerle Joseph R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O INTERNATIONAL COAL GROUP, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>300 CORPORATE CENTRE DRIVE</rptOwnerStreet2>
            <rptOwnerCity>SCOTT DEPOT</rptOwnerCity>
            <rptOwnerState>WV</rptOwnerState>
            <rptOwnerZipCode>25560</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Accounting Officer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2011-02-22</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2475</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>23844</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Employee Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>9.09</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2011-02-22</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>6617</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2021-02-22</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>6617</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6617</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Represents a restricted stock (RS) grant of 2,475 shares of common stock, the restrictions on such shares will lapse in equal installments of 619 shares on April 30, 2012, 2013 and 2014 and 618 shares on April 30, 2015.</footnote>
        <footnote id="F2">Includes (a) RS grant of 900 shares, the restrictions on 675 have lapsed and the restrictions on the remaining 225 will lapse on June 30, 2011; (b) RS grant of 900 shares, the restrictions on 450 have lapsed and the restrictions on the remaining 450 will lapse in equal installments of 225 on March 25,  2011 and 2012; (c) RS grant of 4,800 shares, the restrictions on 3,600 have lapsed and the restrictions on the remaining 1,200 will lapse on June 30, 2011; (d) RS grant of 7,669 shares, the restrictions on 1,917 have lapsed and the remaining 5,752 will lapse in equal installments of 1,917 on April 30, 2011 and 2012 and 1,918 on April 30, 2013; (e) RS grant of 3,000 shares, the restrictions will lapse in equal installments of 750 on April 30, 2011, 2012, 2013 and 2014; (f) a RS grant of 2,475 shares, the restrictions will lapse in equal installments of 619 on April 30, 2012, 2013 and 2014 and 618 on April 30, 2015.</footnote>
        <footnote id="F3">Represents stock options for 6,617 shares of common stock, which will vest in equal installments of 1,654 shares on April 30, 2012, 2013 and 2014 and 1,655 shares on April 30, 2015.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Joseph R. Beckerle</signatureName>
        <signatureDate>2011-02-24</signatureDate>
    </ownerSignature>
</ownershipDocument>
