<?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>0001500579</rptOwnerCik>
            <rptOwnerName>Patterson Gary</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>SVP, Operations WV-MD Region</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>11068</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>58409</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>29590</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>29590</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>29590</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Represents a restricted stock (RS) grant of 11,068 shares of common stock, the restrictions on such shares will lapse in equal installments of 2,767 shares on April 30, 2012, 2013, 2014 and 2015.</footnote>
        <footnote id="F2">Includes (a) a RS grant of 8,000 shares, the restrictions on 2,000 have lapsed of which 659 have been withheld to satisfy tax withholdings; restrictions on the remaining 6,000 will lapse in equal installments of 2,000 on April 30, 2011, 2012 and 2013; (b) a RS grant of 3,000 shares, the restrictions will lapse in equal installments of 750 on April 30, 2011, 2012, 2013 and 2014; (c) a RS grant of 37,000 shares, the restrictions will lapse in equal installments of 9,250 on April 30, 2011, 2012, 2013 and 2014; (d) a RS grant of 11,068 shares, the restrictions will lapse in equal installments of 2,767 on April 30, 2012, 2013, 2014 and 2015.</footnote>
        <footnote id="F3">Represents stock options for 29,590 shares of common stock, which will vest in equal installments of 7,398 shares on April 30, 2012 and 2013 and 7,397 shares on April 30, 2014 and 2015.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Roger L. Nicholson, Attorney in Fact for Gary A. Patterson</signatureName>
        <signatureDate>2011-02-24</signatureDate>
    </ownerSignature>
</ownershipDocument>
