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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-03-03</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001333440</rptOwnerCik>
            <rptOwnerName>Snavely Charles Goble</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, WV &amp; Northern Region Ops</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2009-03-03</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>29759</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>91259</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>1.52</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2009-03-03</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>101453</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2019-03-03</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>101453</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>101453</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Represents a restricted stock grant of 29,759 shares of common stock, the restriction on such shares will lapse in equal installments of 7,440 shares on April 30, 2010, 2011 and 2012 and 7,439 shares on April 30, 2013.</footnote>
        <footnote id="F2">Includes (a) a restricted stock grant of 6,000 shares of common stock, the restrictions on which 3,000 have lapsed and the restrictions on the remaining 3,000 will lapse in equal installments of 1,500 shares on June 30, 2009 and 2010; (b) a restricted stock grant of 6,000 shares of common stock, the restrictions on which 1,500 have lapsed and the restrictions on the remaining 4,500 will lapse in equal installments of 1,500 shares on June 30, 2009, 2010 and 2011; (c) a restricted stock grant of 6,000 shares of common stock, the restrictions on which will lapse in equal installments of 1,500 shares on March 25, 2009, 2010, 2011 and 2012; and (d) a restricted stock grant of 29,759 shares of common stock, the restrictions on which will lapse in equal installments of 7,440 shares on April 30, 2010, 2011 and 2012 and 7,439 shares on April 30, 2013.</footnote>
        <footnote id="F3">Represents stock options for 101,453 shares of common stock, which will vest in equal installments of 25,363 shares on April 30, 2010, 2011 and 2012 and 25,364 shares on April 30, 2013.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Roger L. Nicholson, Attorney-in-fact for Charles Goble Snavely</signatureName>
        <signatureDate>2009-03-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
