Here are some documents produced by the Illinois Legislative Process:
Westlaw & Lexis: Westlaw has scraped most of the information you can obtain from the ILGA website including: code, session laws, bill status pages, bill versions. and floor debates. Lexis has the same except floor debates. Both
HeinOnline: Hein has session laws for most states going back to pre-statehood days as well as historical versions of code.
Illinois General Assembly: The Illinois legislature's website, ILGA.GOV, provides public access to statutory code, session laws, bills status, committee reports, floor debates, and gives directions for obtaining audio of house committee hearings.
The Illinois Legislative Reference Bureau staff has create this guide to help with Researching Legislative History.