You'll need to talk to some insiders familiar with IL's different prisons.
Apparently the state has a work camp system for minimum security prisoners, and i now that in other states those usually aren't too bad and they keep the inmates busy(My BIL was in one for a while in NJ). But he has to make sure he doesn't mess up or get in a fight or something and wind up in an actual prison in the general population. That can be some really nasty stuff with gangs, sexual abuse, etc.
Jail is usually much more boring, there may be county work programs and such as well, but there is also usually less chance of getting in further trouble.

