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I-90 is certainly one route that will get you to Yellowstone and there are any number of great attractions along it besides just Mount Rushmore. But you should also be considering taking an entirely different route on the way home to maximize the number of new things that you get to see on this trip. One such alternate route would be essentially I-80 through Wyoming and Nebraska. You can, of course, do either route in either direction.

Along I-90 highlights would include Wisconsin Dells and Circus World Museum in Wisconsin (particularly if you have young children), Great River Bluffs State Park along the Mississippi River, the falls and Great Plains Zoo in Sioux Falls, the Corn Palace in Mitchell SD, Badlands National Park, and Little Bighorn National Battlefield. And those are in addition to the many sites near Mount Rushmore including Wind and Jewel Caves, the Crazy Horse Memorial and Devils Tower.

Along I-80 highlights would include Starved Rock and Matthiessen State Parks on the Illinois River, the Amana Colonies near Cedar Rapids IA, the Lewis and Clark Trail Headquarters in Omaha, the many Oregon Trail sites and landmarks along the Platte River in Nebraska, the Wind River Range along US-287 up into Grand Teton National Park, and the Rockefeller Memorial Parkway from there up into Yellowstone.

Note that all those sites are west of Chicago. Between Cleveland and Chicago I-90 and I-80 are duplexed, i.e. they share the same roadbed. Also You can choose to treat Chicago either as a great place to stop and explore its many fine museums or as a traffic nightmare to be gotten through or around as best as you can. Both attitudes are equally correct.

AZBuck