Where in Illinois? Cliffs insane terrain is Southwest of Chicago, small park and mostly mud. Badlands in Indiana is probably the closest decent place to wheel. I'm not too familiar with southern IL, maybe there's some stuff down there.
Maybe something forest roadish in SE IL, otherwise it's The Cliffs Insane Terrain Park. The Cliffs is about 2 hrs straight south of Rockford just east of La Salle outside of Marseilles, IL.
Sloppy when it's wet, decent when it's dry. I haven't been there in 5-6 years.
The Badlands Off-Road Park in Attica, IN just NE of Danville, IL about 20min.
Lots of terrain options and has a quarry that you can crawl around in and pretend you are home