According to the Illinois Vehicle Code (specifically sections 5/100 - 5/601) it talks about how no person shall drive any motor vehicle upon a highway in this state unless such person has a valid license or permit.
Section 5/6-601 states the main penalties for driving without a license in Illinois. Here it says that unless another penalty is in the law every person convicted of a petty offense for the violation of this Chapter of law shall be punished by a fine of not more than $500. However the next subsection states for unlicensed driving it is a Class B misdemeanor if the person has never been issued a driver’s license. It is a Class A misdemeanor if the person failed to obtain a driver’s license or permit after expiration of a period of revocation.
It goes on to state that in addition to other penalties imposed under IL law, any person in violation of this section who is also in violation of the Illinois mandatory insurance requirements shall have his or her motor vehicle immediately impounded by the arresting law enforcement officer. The motor vehicle may be release to any licensed driver upon showing proof of insurance for the car and notarized written consent for the release by the vehicle's owner.
So for an illegal immigrant in Chicago, Illinois the penalty for driving without a license appears to fall under a Class B misdemeanor charge. This type of charge comes with penalties of a fine up to $1000 and/or 6 months in jail. Just for reference, a Class A misdemeanor comes with a fine of up to $2500 and possible 12 months imprisonment.
Since it is likely an illegal immigrant would also be uninsured for the vehicle they are driving, since they do not have a driver’s license to use for rating purposes with an insurer, then they would like have their car impounded and also be ticketed for driving without insurance. The penalties for this offense includes fine of $500 to $1000 and suspension of the driver’s license but since the uninsured illegal did not have a license already this penalty would likely mean nothing to them unless at some later date they applied to get a driver's license.
As you likely are aware, bills have come up in Illinois, but have not been passed, to allow illegal immigrants to get a certificate to drive since they are unable to get a driver's license. The Vehicle Code of Illinois is updated or amended regularly so you can check with the Secretary of State to find out more about the penalties regarding driving without a valid license as an illegal immigrant and if any current state bills will affect the current laws on the books.