I grew up in Chicago and live in a western suburb...the first two weeks of Oct. are beautiful here...downtown is fun on the weekends, with Navy Pier, and walking in Millenium Park. There are many old buildings downtown that have beautiful artitectural designs on them. There are many museums in Chicago, too, but you have to pay to get in. Look on line for things to do in the city.
But you could stay out in the western part of the area and take a train downtown; that way you're not staying in the crowded area (where it's also expensive). In Naperville, there's Naper Settlement, which is a historic site that has buildings from the 1800s...such as a school room, a log cabin, and a fort. The volunteers dress up in period dress. There's also a mansion that is set up from the same time period. We also have a historic farm in Naperville. I'm sure if you go on Naperville's website, you can see some of those things.
There's Morton arboretum nearby (in Lisle), and Brookfield Zoo has areas that are natural habitats for certain zones, such as tropic world for apes/monkeys.
Starved Rock state park is about 1-2 hrs from Naperville; it is a beautiful park.

There's many things to do in the area...just go online and you'll be informed...