35 ILCS 200/21-45
In the event no tax bill was issued as provided in Section 21-30, on any property in any previous year for any reason, one tax bill shall be prepared and mailed by July 1 of the year subsequent to the year in which no tax bill was issued, and taxes on that property for that year only shall bear interest after the first day of August of that year. In counties with fewer than 3,000,000 inhabitants, interest shall accrue at the rate of 1 1/2% per month or portion thereof until paid or forfeited. In counties with 3,000,000 or more inhabitants, if the taxes are for a tax year before tax year 2023, then interest shall accrue at the rate of 1.5% per month, or portion thereof, until paid or forfeited. In counties with 3,000,000 or more inhabitants, if the taxes are for the 2023 tax year or any tax year thereafter, then interest shall accrue at the rate of 0.75% per month, or portion thereof, until paid or forfeited.
35 ILCS 200/21-45