We like Jellystone - Millbrook.
It's a little expensive, but it's a really nice park. We like it for opening the camper since we live only 35 mins from it :-)
They have a lot of activities for the kids.
http://www.jellystonechicago.com
It's close to 80 but it will take you a little under an hour to get downtown from there. You could also drive into joliet to take the train.
Windy city is gone. There is another one just outside New Lenox, it is right on 80, I pass it all the time, but can't remember the name. Though it looks pretty dumpy and would be noisy.
Jen