Illinois only requires emissions testing in certain counties, mainly the Chicago area and the Metro East region near St. Louis. If your car is registered in Cook County or one of the surrounding collar counties, you'll need a test every two years. The rest of the state doesn't have a testing requirement at all.
For cars built after 1996, the test plugs into your OBD-II port so the technician can read the onboard computer for trouble codes and confirm the emissions monitors are ready. Older vehicles still go through tailpipe testing. The Illinois EPA runs the program and keeps quality control tight across its certified stations.
How Much is a Smog Check in Illinois?
Illinois keeps it simple: the test costs a flat $20 at most stations, whether you're in Chicago, suburban Cook County, or the Metro East. That state-set fee takes the guesswork out of pricing, and it makes Illinois one of the cheaper states to get tested in.
If you fail, you get a free retest within 30 days once you've made repairs. Since the schedule is every two years rather than yearly, you're only paying this every other year, which softens the cost. Still, don't leave it until your registration deadline, or you'll be stuck in the peak-season rush.
Tips for Paying Less on a Smog Check
With a fixed $20 fee, price isn't really the variable here, wait times are. State-run Air Team stations tend to have longer lines during busy periods, but they can't sell you repairs, so there's no upsell pressure. That makes them a good choice if your car is likely to pass.
Private test-and-repair stations charge the same $20 base fee but can also fix your car if it fails. Convenient, but keep in mind a shop that profits from repairs has a built-in reason to find problems. Plenty of drivers prefer to fail at a test-only station, then get repair quotes from an independent mechanic.
Aim for off-peak hours, weekday mid-mornings or early afternoons, to skip the worst lines at busy stations around Chicago and Naperville. The Illinois EPA website posts real-time wait estimates for many locations, so check before you head out. Booking an appointment where available is the surest way to avoid sitting around, especially in summer when renewal deadlines bunch up.