Your post isn't entirely clear as to if you are looking for places to camp, or interesting places to visit.
The Shawnee National Forest seems to be a well kept secret. Few people, even in Northern Illinois know much about it, and many don't even know that it even exists. The area was never glaciated, so the terrain is nothing at all like the corn field in the rest of the state. We have never made reservations there, and never had trouble finding a camp site.
It surprises many to learn that Cairo, IL is farther south than Richmond, VA. As a result, much of the Cache River Basin is a Cypress/Tupelo swamp that looks like it belongs in southern Louisiana.
X2 for Garden of the Gods National Recreation Area. It is an interesting place, and their Pharaoh camp ground has some great views.
Our favorite place to camp is the Train of Tears State Forest. The campground there was constructed by the CCC. The road through the camp ground climbs up to a ridge, and then runs along the ridge. Most of the ridge is too narrow for camp sites, and in spots where it does widen out, there is only room for one site. In many of the sites, the next nearest site may be 1/4 mile away. Each site has a picnic table and outhouse. Several of the sites have 3 sided stone and log shelters, with stone fireplace. In one 3 day period camping there, se saw more deer and more wild turkeys than people.
As I mentioned, much of the Cache River Basin is a Cypress/Tupelo swamp. A visit to the Cache River Visitor Center is a good place to start. The hike to Heron Pond (more a swamp than a pond) is interesting, with a boardwalk into the swamp. Horseshoe Lake is an interesting paddle. In one day on the lake, we saw more Bald Eagles than people. That includes the two nights we spent in the campground there.
If you enjoy hiking the loop trail a into The Little Grand Canyon is a must. The view is fantastic. That they managed to get a trail constructed there, is amazing. Om the lower part of the trail, you scramble down a (now dry) waterfall. You walk about 1/3 along the bottom, and then up another dry water fall.
Photos:
1. Pharaoh camp ground, Garden of the Gods.
2. Camel Rock, Garden of the Gods.
3. Trail of Tears State Forest, camp site.
4. Trail of Tears State Forest, camp site.
5. Horseshoe Lake, Cache River Basin.
6. Looking down at a soaring Turkey Vulture.