Not many sites that big. We camped there in our 34' TT (not quite as high as a 5er) and barely fit in our site (#12). That was one of the biggest ones there, and I noted in my camping log book that it was the best site for our rig. Sorry, I didn't note any other sites except one that was smaller.
That said, it's a beautiful park. Most sites are in a stand of pines, nice & shady (important in a hot humid summer). The "new" bathhouse (probably 5-6 years old) was a much-needed addition, and was pretty nice in 2012.
The IL SP website may note site length, which will be very helpful if they do. Good luck!
2020 Toyota Tundra CrewMax 5.7L V8 w/ tow pkg, Equal-i-zer
2020 Lance 2375