<ownershipDocument><schemaVersion>X0201</schemaVersion>    <documentType>4</documentType><periodOfReport>2003-12-19</periodOfReport><notSubjectToSection16>0</notSubjectToSection16><issuer><issuerCik>0001031296</issuerCik><issuerName>FIRSTENERGY CORP</issuerName>        <issuerTradingSymbol>FE</issuerTradingSymbol></issuer><reportingOwner><reportingOwnerId><rptOwnerCik>0001237010</rptOwnerCik><rptOwnerName>ADDISON PAUL T</rptOwnerName></reportingOwnerId><reportingOwnerAddress><rptOwnerStreet1>76 SOUTH MAIN STREET</rptOwnerStreet1><rptOwnerStreet2></rptOwnerStreet2><rptOwnerCity>AKRON</rptOwnerCity><rptOwnerState>OH</rptOwnerState><rptOwnerZipCode>44308</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 Units</value></securityTitle><conversionOrExercisePrice><value>1</value><footnoteId id="F1"/></conversionOrExercisePrice><transactionDate><value>2003-12-19</value></transactionDate><deemedExecutionDate><value>2003-12-19</value></deemedExecutionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>127</value></transactionShares><transactionPricePerShare><value>34.69</value></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>127</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>848.3503</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>I</value></directOrIndirectOwnership><natureOfOwnership><value>By State Street</value></natureOfOwnership></ownershipNature></derivativeTransaction></derivativeTable><footnotes><footnote id="F1">1 for 1</footnote><footnote id="F2">In accordance with the terms and conditions of the FirstEnergy Corp. Deferred Compensation plan for Outside Directors.</footnote></footnotes><ownerSignature><signatureName>David W. Whitehead, POA</signatureName><signatureDate>2003-12-19</signatureDate></ownerSignature></ownershipDocument>

