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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-02-22</periodOfReport>

    <issuer>
        <issuerCik>0000097216</issuerCik>
        <issuerName>TEREX CORP</issuerName>
        <issuerTradingSymbol>TEX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001140109</rptOwnerCik>
            <rptOwnerName>DEFEO RONALD M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>TEREX CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>500 POST ROAD EAST, SUITE 320</rptOwnerStreet2>
            <rptOwnerCity>WESTPORT</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06880</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chairman, President &amp; CEO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2006-02-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>7</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>77.96</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>337324</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2006-02-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>I</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>0</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3514</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>401(k) plan</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Employee Stock Option (right to buy)</value>
                <footnoteId id="F3"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>25.375</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-02-24</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>60000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2002-02-24</value>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F4"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, par value $.01</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>60000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>60000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Shares purchased through payroll deductions through the Company's Employee Stock Purchase Plan.</footnote>
        <footnote id="F2">Represents shares beneficially owned as of February 22, 2006.</footnote>
        <footnote id="F3">Stock option granted on February 24, 1999, pursuant to one of the Company's long-term incentive plans, with a seven year term.</footnote>
        <footnote id="F4">As a result of the Company's previously disclosed restatement process, the Company determined that all Terex employees, former employees and directors are unable to exercise any options to purchase Terex common stock until the Company is current in filing all of its periodic reports with the SEC.  Accordingly, the Company's Board of Directors has determined that the Company will honor any options to purchase shares of the Company's common stock that have been granted pursuant to any of the Company's long-term incentive plans, which options otherwise would have expired unexercised solely because the individuals owning such options are currently unable to exercise such options prior to their expiration due to the Company's delay in timely filing its periodic reports with the SEC.  This limited accommodation will be for a period of thirty (30) days from the date that the Company determines that it is first permissible to exercise such options.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Ronald M. DeFeo</signatureName>
        <signatureDate>2006-02-24</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2006-02-22
0000097216
TEREX CORP
TEX
0001140109
DEFEO RONALD M
TEREX CORPORATION
500 POST ROAD EAST, SUITE 320
WESTPORT
CT
06880
1
1
0
0
Chairman, President & CEO
Common Stock, par value $.01
2006-02-22
4
P
0
7
77.96
A
337324
D
Common Stock, par value $.01
2006-02-22
5
I
0
0
0
A
3514
I
401(k) plan
Employee Stock Option (right to buy)
25.375
2006-02-24
4
A
0
60000
0
A
2002-02-24
Common Stock, par value $.01
60000
60000
D
Shares purchased through payroll deductions through the Company's Employee Stock Purchase Plan.
Represents shares beneficially owned as of February 22, 2006.
Stock option granted on February 24, 1999, pursuant to one of the Company's long-term incentive plans, with a seven year term.
As a result of the Company's previously disclosed restatement process, the Company determined that all Terex employees, former employees and directors are unable to exercise any options to purchase Terex common stock until the Company is current in filing all of its periodic reports with the SEC.  Accordingly, the Company's Board of Directors has determined that the Company will honor any options to purchase shares of the Company's common stock that have been granted pursuant to any of the Company's long-term incentive plans, which options otherwise would have expired unexercised solely because the individuals owning such options are currently unable to exercise such options prior to their expiration due to the Company's delay in timely filing its periodic reports with the SEC.  This limited accommodation will be for a period of thirty (30) days from the date that the Company determines that it is first permissible to exercise such options.
/s/ Ronald M. DeFeo
2006-02-24