<SUBMISSION>
<ACCESSION-NUMBER>0001181431-04-047577
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20041011
<FILING-DATE>20041013
<DATE-OF-FILING-DATE-CHANGE>20041013
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>SEI INVESTMENTS CO
<CIK>0000350894
<ASSIGNED-SIC>6211
<IRS-NUMBER>231707341
<STATE-OF-INCORPORATION>PA
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>1 FREEDOM VALLEY DRIVE
<CITY>OAKS
<STATE>PA
<ZIP>19456-1100
<PHONE>6106761000
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>1 FREEDOM VALLEY DRIVE
<CITY>OAKS
<STATE>PA
<ZIP>19456-1100
</MAIL-ADDRESS>
<FORMER-COMPANY>
<FORMER-CONFORMED-NAME>SEI INVESTMENT CO
<DATE-CHANGED>20040806
</FORMER-COMPANY>
<FORMER-COMPANY>
<FORMER-CONFORMED-NAME>SEI CORP
<DATE-CHANGED>19920703
</FORMER-COMPANY>
</ISSUER>
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>SMITH THOMAS W
<CIK>0000926688
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>000-10200
<FILM-NUMBER>041077533
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>323 RAILROAD AVENUE
<CITY>GREENWICH
<STATE>CT
<ZIP>06830
<PHONE>2036611200
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>323 RAILROAD AVENUE
<CITY>GREENWICH
<STATE>CT
<ZIP>06830
</MAIL-ADDRESS>
<FORMER-NAME>
<FORMER-CONFORMED-NAME>THOMAS W SMITH
<DATE-CHANGED>19940713
</FORMER-NAME>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>rrd54846.xml
<DESCRIPTION>FORM 4 REFLECTING PARTNERSHIP DISTRIBUTIONS BY IDOYA PARTNERS AND PRESCOTT INTERNATIONAL PARTNERS
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-10-11</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000350894</issuerCik>
        <issuerName>SEI INVESTMENTS CO</issuerName>
        <issuerTradingSymbol>SEIC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000926688</rptOwnerCik>
            <rptOwnerName>SMITH THOMAS W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>323 RAILROAD AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>GREENWICH</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06830</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2004-10-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>7123</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>156777</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Prescott International Partners</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2004-10-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F3"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>94921</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2689193</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F4"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Idoya Partners</value>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Represents a partnership distribution by Prescott International Partners, without consideration, in accordance with the terms of its limited partnership agreement.</footnote>
        <footnote id="F2">These shares are owned directly by Prescott International Partners (&quot;PIP&quot;), a private investment limited partnership, and indirectly by the Reporting Person as general partner of PIP.  The Reporting Person disclaims beneficial ownership of these shares in excess of his pecuniary interest in such shares under Rule 16a-1(a)(2)(ii)(B). The address for PIP is 323 Railroad Avenue, Greenwich, CT 06830</footnote>
        <footnote id="F3">Represents a partnership distribution by Idoya Partners, without consideration, in accordance with the terms of its limited partnership agreement.</footnote>
        <footnote id="F4">These shares are owned directly by Idoya Partners (&quot;Idoya&quot;), a private investment limited partnership, and indirectly by the Reporting Person as general partner of Idoya.  The Reporting Person disclaims beneficial ownership of these shares in excess of his pecuniary interest in such shares under Rule 16a-1(a)(2)(ii)(B). The address for Idoya is 323 Railroad Avenue, Greenwich, CT 06830</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Thomas W. Smith</signatureName>
        <signatureDate>2004-10-13</signatureDate>
    </ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
