Peggy Notebaert Nature Museum in Chicago
One place that I really think that everyone going through Illinois should visit is The Peggy Notebaert Nature Museum (http://www.naturemuseum.org/), in Chicago.
It is pretty much right across the street from the Lincoln Park Zoo, so it is conceivable to visit both in one day, although I think when I went with my wife and almost three-year-old son, we just made a day trip out of the nature museum.
There are a lot of different exhibits in the museum, well-suited to many ages and interests, although honestly, I think the only place we really looked at was the butterfly garden. The garden was really my main reason for wanting to bring my family there. And it is absolutely beautiful!
Inside a mildly tropical setting (make sure you do not dress too warmly, or at least bring layers if you visit in the winter, as it can be a little humid inside), there is a beautiful walk-through garden/greenhouse. There are gorgeous flowers and trees there, which of course serve as home for the myriad butterflies, as well as some exotic birds. There are all types of butterflies there, and you can spend the day just sitting around in the garden and watching them flutter by (our son thought all the colorful fluttering was hilarious).
There are a number of little stands and bird baths and the like that butterflies readily perch on, so it is very easy to get a great look at them. Cameras are allowed, so you can take photographs of them as well.
If you are one of those people (like me!) who has dreams of being landed on by butterflies, a visit to the garden is a chance to make that dream come true. Just don't try to touch them! I think there were some signs strongly discouraging that.
It is almost impossible to not be landed on, though; the chance is so great that there is a small, mirrored room on the way out so that you can check to make sure you aren’t leaving with any of your new-found winged friends.
So, if you are in Illinois and Chicago specifically, I really recommend a trip to the nature museum (if only to the butterfly haven). It is a beautiful place to go, and the kind of thing everyone should do at least once.