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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-02-15</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000003673</issuerCik>
        <issuerName>ALLEGHENY ENERGY, INC</issuerName>
        <issuerTradingSymbol>AYE</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001035140</rptOwnerCik>
            <rptOwnerName>BALDWIN H FURLONG</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ALLEGHENY ENERGY, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>800 CABIN HILL DRIVE</rptOwnerStreet2>
            <rptOwnerCity>GREENSBURG</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>15601</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2011-02-15</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>355.297</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>25.80</value>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>355.297</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10363.87</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Under the Issuer's Revised Plan for Deferral of Compensation of Directors, non-employee members of the Issuer's Board of Directors (the &quot;Board&quot;)may elect to defer receipt of all or a part of the cash portion of the director fees to which they become entitled in connection with their service on the Board and may opt to invest all or a portion of any such deferred amounts into a phantom stock fund maintained by the Issuer.  Mr. Baldwin has elected to defer receipt of all of the cash portion of the fees payable to him and to invest such deferred amounts in the Issuer's phantom stock fund.</footnote>
        <footnote id="F2">Each unit of phantom stock is the economic equivalent of one share of the Issuer's common stock, par value $1.25 per share (the &quot;Common Stock&quot;).  The units of phantom stock are payable in cash upon the termination of Mr. Baldwin's service on the Board.</footnote>
        <footnote id="F3">The average of the high and low prices on the New York Stock Exchange of one share of the Issuer's Common Stock on the applicable transaction date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Amanda J. Skov  Attorney-in-Fact</signatureName>
        <signatureDate>2011-02-16</signatureDate>
    </ownerSignature>
</ownershipDocument>
