Our reservation systems in IL are straight up wierd- and sometimes disappointing.
IL state CG's accept reservations- but only 7 days in advance, you have to pay in advance, and, its a minimum 2 night stay. And there are no refunds on the reservation.
But, you can view most sites/loops and see what is already taken and whats still left.
Privately owned CG's have their own reservation/site rules and they vary from place to place. Most share the 2 night rule, but drive-ups can stay only one night if you wish.
The 'first come' rule is always a gamble- but saves a few bucks. And in our many years of camping in IL, we've never seen a full campground. (Admittedly, we do stay away from major holiday weekends for camping due to the crowding and noise- so we haven't experienced those in many years.)
Camping is just a relaxing way to practice for being homeless. :Flag:
2009 JKU TV (Its a Jeep thing...you wouldn't understand!)
2000 Quest 8U PUP