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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-10-10</periodOfReport>

    <issuer>
        <issuerCik>0000104207</issuerCik>
        <issuerName>WALGREEN CO</issuerName>
        <issuerTradingSymbol>WAG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001197069</rptOwnerCik>
            <rptOwnerName>MCNALLY ALAN G</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>200 WILMOT ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>DEERFIELD</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60015</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chairman and Acting CEO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Walgreen Co. Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-10-10</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>26600</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>53191</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Employee Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>23.22</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2008-10-10</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>120000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>120000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>120000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Shares underlying Restricted Stock Units.  13,300 shares vest on the earlier of April 10, 2009 or the date on which a new chief executive officer of the registrant begins working.  13,300 shares vest in installments of 1,108 shares at the end of each month of continued employment as chief executive officer following April 10, 2009.</footnote>
        <footnote id="F2">Options to acquire 60,000 shares vest on the earlier of April 10, 2009 or the date on which a new chief executive officer of the registrant begins working.  Options to acquire 60,000 vest in installments of 5,000 shares at the end of each month of the reporting person's employment as chief executive officer following April 10, 2009.</footnote>
        <footnote id="F3">Vested options remain exercisable until five years after the later of the reporting person's termination of employment or Board service, provided that the options may not be exercised after the 10-year anniversary of the grant date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Yuri Rozenfeld, attorney-in-fact</signatureName>
        <signatureDate>2008-10-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0303
4
2008-10-10
0000104207
WALGREEN CO
WAG
0001197069
MCNALLY ALAN G
200 WILMOT ROAD
DEERFIELD
IL
60015
1
1
0
0
Chairman and Acting CEO
Walgreen Co. Common Stock
2008-10-10
4
A
0
26600
0
A
53191
D
Employee Stock Option (right to buy)
23.22
2008-10-10
4
A
0
120000
0
A
Common Stock
120000
120000
D
Shares underlying Restricted Stock Units.  13,300 shares vest on the earlier of April 10, 2009 or the date on which a new chief executive officer of the registrant begins working.  13,300 shares vest in installments of 1,108 shares at the end of each month of continued employment as chief executive officer following April 10, 2009.
Options to acquire 60,000 shares vest on the earlier of April 10, 2009 or the date on which a new chief executive officer of the registrant begins working.  Options to acquire 60,000 vest in installments of 5,000 shares at the end of each month of the reporting person's employment as chief executive officer following April 10, 2009.
Vested options remain exercisable until five years after the later of the reporting person's termination of employment or Board service, provided that the options may not be exercised after the 10-year anniversary of the grant date.
Yuri Rozenfeld, attorney-in-fact
2008-10-15