Census Records for Illinois Territory.
The State of Illinois also has census data on slaves:
Illinois State Archives, Data on Servitude.
The Illinois Black Code law was fetched by a FReeper in a discussion about such codes (and black internal migrations postwar) in a 2004 or 2005 ACW thread here on FR. If I have time, I'll go look for it. Too bad our FReepmail is purged periodically, we had a lot of internal discussions about sources.
Source: Wiki article. (Still under construction, w/ comment called for.)
Metasearch using Ask.com, Dogpile, or similar, and try "Illinois Black Code" as the search key; you'll get abundant returns from various articles both scholarly and general press articles (one about the history of Illinois race politics from the beginnings to Obama).