Midwest routes

Illinois - Starved Rock State Park. You should be aware that there are toll roads near the Chicago area. Expect lots of truck traffic around the south side of Lake Michigan on I-80. I would advise going around Chicago, not through it.
Wisconsin - The waterparks in the Dells area are a great place to meet up with family
Michigan - I like Mackinac Island, the Ludington area, and Warren Dunes
Indiana - Indiana Dunes

Try this site: https://midwestweekends.com/plan_a_trip/touring/lake_michigan/lake_michigan_circle_tour.html
You could certainly spend a couple of days in Door County, WI where we spend at least a week every summer. Stay at the Egg Harbor RV Resort but plan ahead. Send for the DC Visitor's Guide for more info.

Starved rock state park is hard to get a spot but is beautiful park.

www.rvparkreveiws.com is a good site for info also free to join

Google Door County WI. It's north of Green Bay. We like that area a lot. Indiana Dunes State Park is another favorite.

If I was to head up to Door County, WI would I then be able to no north and cut over and come back down into Michigan? Should I start in Indiana and then head over up through Michigan and then down through Wisconsin?

If you go to Door County, you can go through Green Bay and swing north into the UP then follow US 2 over to the Mackinac Bridge and then head south to Traverse Bay. There are a marked set of roads that make up the Lake Michigan Circle Drive. We did that last year and it was a really nice trip. Took us 2 weeks to make it all the way around.

If you are by South Bend, IN stop at the KOA in South Bend. The community of Amish in Shipshewanna, IN and Norte Dame are nice places to visit. There is a very nice Italian restaurant right outside of the campground gate,the campground is clean and quiet.

From Wisconsin Dells area, you could go into MI upper peninsula , visit copper harbor, tequemonon falls, mackinaw island, pictures rocks, then cross the Mackinaw bridge into the lower peninsula. You would totally miss Chicago this way. Lower peninsula we are partial to the Western side/shore of Lake Michigan. There are many many campgrounds in Michigan.

Generally the scenic areas are close to lakes (including the Great Lakes) and rivers.

The Mississippi valley is deeper from the Illinois Palisades State Park and north. The SW corner of Wisconsin is hillier. Otherwise Illinois and Wisconsin are pretty flat.

Wisconsin Dells is a gorge stretch of the Wisconsin River, but very touristy. I like the Devils Lake area in the Bariboo Mtns better.

Door County is a peninsula with Lake Michigan on all sides. I like going all the way to Rock Island State Park. Otherwise it's hard to stay close to Lake Michigan on the Wisconsin side. I'm less familiar with the Michigan side of the Lake.

Northern Wisconsin and Minnesota have lots of lakes and woods. The Lake Superior shore is scenic, especially the NW part north of Duluth. The circle route around this Lake gets more remote.

State parks are a pretty good guide to the scenic parts of these states.

Devil's Lake State Park is beautiful and the Dells Upper River Scenic boat tour is worth the money.