Devil's Lake is great - we have camped there a few times.
In the fall we go near South Bend, Indiana to Potato Creek State Park. Nice State Park, bike trails, canoe rentals. We go apple picking.
Last August we went to Sleeping Bear Dune National Lakeshore in Michigan. It was awesome and we are going back this August. I guess it is about a 5 hour drive.
In Southern IL, Giant City has great hiking. There is alot of good camping near Carbondale.
In Indiana we also like Turkey Run State Park. It is alot like Starved Rock, but bigger. Great hiking. Close to home, my parents used to always take us camping at Chain O Lakes State park (the Lake Co/McHenry Co border). When we go that way, we go to Kettle Moraine State Park in Wisconsin. ALso close to home is Apple River State Park (NW toward Rockford).
Have fun checking places out, but reserve camp sites early. You may find that sites are already reserved for most summer weekends. The sites that we have in Michigan for August are already all taken. Here is the IL State Park website:http://dnr.state.il.us/lands/Landmgt...ping/index.htm