PACER
Plus
The U.S. Party/Case Index is a national index for U.S. district, bankruptcy, and appellate courts.  The system serves as a locator index for PACER. You may conduct nationwide searches to determine whether or not a party is involved in federal litigation.  All but a few circuit courts are contained in this index.

Watch this 7.5 minute video demo of the USPCI put together by The Virtual Chase.
Federal Courts, Plus State Court Access
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Hints:
- The USPCI doesn't use fuzzy logic.  Party names are entered using many variations by court clerks in different courts.  For example, doing a search for "The Jones" will only find cases involving "The Jones Company", and "The Jones Corporation".  It will NOT find "Jones Company" entered as a party on a docket sheet.

- After logging in with your PACER account and searching the USPCI, all results are linked to the appropriate CM/ECF courts.  There is no need to login again, you can drill down from case listings, to docket sheet, to filings.