You are not required to take particular classes if you are older than 18. You only have to find someone to teach you how to drive. The procedure to obtain a drivers license will be the same as explained above. Most people in the U.S. learn how to drive at age 15 to 17, while they are in school. Therefore, driving schools for adults are not as common as they may be in your home country.
Some high schools offer driver education classes for adults, too.
To find out about classes you should check with a local high school, the school superintendent's office, a community college or a commercial driving school. You must use private parking lots and driveways instead. If you do not drive and do not want to learn how to drive, you should apply for an identification card that you can use as picture ID, just like everybody else uses their driver's license. Carrying around an Illinois identification card is much more convenient than taking your passport with you at all time.