10 ILCS 5/6-105
A person must vote for the first time in person and not a vote by mail ballot if the person registered to vote by mail, unless the person first provides the appropriate election authority with sufficient proof of identity and the election authority verifies the person's proof of identity. Sufficient proof of identity shall be demonstrated by submission of the person's driver's license number or State identification card number or, if the person does not have either of those, verification by the last 4 digits of the person's social security number, a copy of a current and valid photo identification, or a copy of a current utility bill, bank statement, paycheck, government check, or other federal, State, or local government document that shows the person's name and address. A person may also demonstrate sufficient proof of identity by submission of a photo identification issued by a college or university accompanied by either a copy of the applicant's contract or lease for a residence or any postmarked mail delivered to the applicant at his or her current residence address. Persons who apply to register to vote by mail but provide inadequate proof of identity to the election authority shall be notified by the election authority that the registration has not been fully completed and that the person remains ineligible to vote by mail or in person until such proof is presented.
10 ILCS 5/6-105