Illinois Statutes Chapter 770. Liens § 95/7.10. Late fees

(a) A reasonable late fee may be imposed and collected by an owner for each service period that an occupant does not pay rent when due under a rental agreement, provided that the due date for the rental payment is not earlier than the day before the first day of the service period to which the rental payment applies. No late payment fee shall be assessed unless the rental fee remains unpaid for at least 5 days after the date specified in the rental agreement for payment of the rental fee.

(b) No late fee may be collected pursuant to this Section unless the amount of that fee and the conditions for imposing that fee are stated in the rental agreement or in an addendum to that agreement.

(c) For purposes of this Section, a late fee of $20 or 20% of the rental fee for each month an occupant does not pay rent, whichever is greater, is deemed reasonable and does not constitute a penalty.

(d) Any reasonable expense incurred as a result of rent collection or lien enforcement by an owner may be charged to the occupant in addition to the late fees permitted by this Section. If any such expenses are charged, they shall be identified on an itemized list that is available to the occupant.