Good suggestion to check tourism sites for each state, and even some of the regions (Adirondacks, Poconos, Mackinaw/Mackinac - incidentally, both spellings pronounced the same way - etc.) Definitely plan to spend a full day (at least) on Mackinac Island; it's a step back in time, and delightful. Ferries are available from both peninsulas of Michigan. (Another good CG for that area is Straits State Park, if you can get a site. Electric hookups only, to my knowledge, but nice, and some sites have a view of the Straits, though probably not of the island.)
We liked the Lake Placid/Whiteface Mt KOA for an Adirondacks base camp - very wooded & pretty, lots to do, and not far from Lake Placid (fun to visit the old Olympic sites there), Saranac Lake and other sites in the area. For the Poconos, one CG not far from there which is rather unique is Driftstone on the Delaware, a private CG with elec & water hookups. Some sites are ENORMOUS, many nicely shaded but plenty of headroom for larger rigs. Family owned. They maintain an old family graveyard in one corner of the CG. Some sites are right on the Delaware River, and you can go canoeing from there. Close to East Stroudsburg, Shawnee-on-Delaware, etc., and reasonably close to some of the better-known waterfalls (Bushkill, etc.) Popular with the locals.
Backing up to the earlier phases of your trip, driving the Great River Road can be interesting, and definitely not the "fast lane." We've driven portions of it in Illinois, Iowa & Wisconsin and enjoyed it. Illinois and Wisconsin both have some very nice state parks along that route, plus there are COE CGs and even a few county parks in Iowa to choose from. (Loved Thomson (COE) CG in Illinois, Miss. Palisades SP in IL, Willow River, Perrot and (our all-time favorite) Wyalusing SPs in WI.)