You will have to visit the Illinois DMV website and search for requirements unless someone who lives there knows. I did a quick search but did not find the answer. But found some very interesting facts.
due to the Governor signing legislation that eliminates the idle exhaust and gas cap tests after January 31, 2012. As part of this legislative change, the following vehicles will be exempt from the emissions test requirement:
Pre-2007 model year gasoline-powered vehicles with a manufacturer's gross vehicle weight rating (GVWR) between 8,501 and 14,000 pounds.
All gasoline-powered vehicles with a manufacturer's GVWR greater than 14,000 pounds (regardless of model year).
Most gasoline-powered cars model year 1996 or newer are subject to emissions testing after they are 4 years old. Heavy duty trucks 2007 or newer are also subject to testing if they weigh between 8,501 pounds and 14,000 pounds. (you guys are lucky).
In many states, failing to obtain a smog certificate makes it illegal to register and operate the vehicle. But in Illinois, it also makes the driver illegal. If you do not get your vehicle tested on schedule, or you do not bring a failing vehicle into compliance, your Illinois driver's license may be suspended.
That right there is harsh, it's like you are connected at the hip to your vehicle.