I stayed at the Jellystone in Sioux Falls as our first stop, then the black hills (Custer SD) for a few days for our second stop. We stayed around Butte MT leaving the black hills for glacier. I stayed in my cousins driveway in the foothills of Kalispell for 4 days, they have 10acres and plenty of moose, bear and other animals roaming around he area.
On the way back we stayed in Billings MT, then again in the black hills (Hill City) for 3 days. Then stayed at a KOA in Rochester MN. And then home. Obviously you will have to ad an extra day for the drive to and from, but it should be a good trip.
Best thing to do with Chicago is take 80 west to 355 north to 90 west. This will take you around all the craziness of the city. 355 never use to connect to 80 until about 7 years ago. Makes it a much more pleasant trip!