When I took exams there last spring, they were held at the Midwest Conference Center 401 W Lake Street Northlake, IL 60164. It's a decent facility, but there isn't enough parking and it's a little tricky to get in and out of the facility. I sent an e-mail to CTS asking about the location prior to the exam because I was travelling from out-of-state and needed to make my hotel reservation. I would suggest you confirm with CTS prior to planning on the address I gave you without verifying it for yourself. For those who haven't been through Illinois' process, the test location is not published information, and it's apparently not always held at the same location, so it's understandable (and perfectly reasonable) that this question is being asked.
Good luck