Heyo

I'm an Irish Dance instructor in Washington State-- I'm taking lessons through a couple of different people as well as teaching my own classes for ages 3-80 (not that I wouldn't take anyone older than 80, they just don't come to my classes!)
Are you looking for any old school? Or recreational classes?
There's a big world of Irish Dancing, from the low "Sean-Nos" dancing (the kind you see old men doing in pubs in Ireland), to Set Dancing (which I can best explain as "Irish Ballroom"), to Irish Ceili (pronounced Kay-lee) Dancing (big group dances--like line and circle dancing), to Modern Irish Step (think Riverdance without the arms!).
I've done all of these, and each has its good and bad points!
If you have no idea what you want, but you don't mind the more "high impact" stuff, I'd say try out Modern Irish Step because you'll get an intro to Soft-shoe and Hardshoe steps as well as a mini-intro to Ceili dancing.
It looks like there is a competitive school called "The Foy School of Irish Dance" in your area (says Des Moines, but I thought I saw something about Schaumburg in the search engine..): They're probably the first people you'll want to check with. The instructor there has a TCRG as well as being part of some good Associations of Irish Dance instructors in the USA.
"Competitive School" doesn't mean that you have to compete, it just means that if you feel like taking the opportunity, you may!
If you feel like taking classes recreationally, they usually provide those for Adults. If they're a purely competitive school, you can still contact them to see if they know of any non-competitive schools in the area that are holding Adult Classes.
A tiny word of warning-- Enrollment usually happens in September and January, and they typically limit the number of classes held in the summer (because people like to vacation!), so you may have to wait until September for a class to be open for you.
Best of luck! And feel free to ask any more questions-- I've got answers for you
