You can search patent assignment documents at the USPTO’s website.
By Erik J. Heels
First published 2/17/2004; LawLawLaw Newsletter; Clock Tower Law Group
In the United States, inventions are applied for in the name of the inventor(s) and then frequently the rights to the inventions are transferred. Assignments are the legal documents used for transferring patent rights, and many of these assignments can now be searched online at the USPTO’s website (http://assignments.uspto.gov/assignments/).