Living in KC and having made the drive to Chicago many times, here's the BEST tip I can give you.
Do NOT take I-70 back to St. Louis and then up I-55 to Chicago. I-70 is a very busy highway, and I-55 is insane during the summer, and the (seemingly) constant road construction is a pain, you can get stuck for an hour or more, easily on I-55 during the summer due to construction or accidents.
Instead take I-35 North to Des Moines, IA (you could do Adventureland, its worth going to, you can usually do the coasters in a couple of hours, or save it for another time) and then head East on I-80 to the Quad Cities (Davenport and Bettendorf , in Iowa; and Rock Island and Moline in Illinois.) From there it's about 6 of one or a half dozen of the other, you can continue on I-80 or I-88 to Chicago. We usually go up I-88, as our family is in the north part of Chicagoland, near Great America. Once you get near Chicago, expect traffic, sometimes it moves, other times you don't.
This is from my personal experience, on a route I travel at least two times a year. You can still be delayed either way, but I feel you're less likely to be delayed going up through Iowa, and it's only a difference of less than 30 miles or so, about 30 more to go north through IA.) It's a long haul, but worth it. Peace.
PS if you're looking for something to do, if you get bored, you can go to Union Station near downtown Kansas City (about 15 minutes away) and check out the Screams of the Past: The First Five Roller Coasters at Worlds of Fun
exhibit with working models of the original five roller coasters from Worlds of Fun along with some coaster artifacts, historic pictures and memorabilia. I know the guy who put the exhibit together.
It's free too.