65 ILCS 5/9-3-22
The ordinance for any improvement to be constructed under this Division 3 may provide that the special assessment to be levied to defray the cost thereof be divided into installments, not more than 20 in number. The first installment of the assessment shall be due and payable on January 2 next after the awarding of the contract for the construction of such improvement. The second installment shall be due one year thereafter, and so on annually, until all installments are paid. It is hereby made the duty of the clerk of the corporate authorities, to file in the office of the clerk of the court in which the assessment was confirmed, a certificate setting forth the date of the awarding of the contract for the construction of the improvement. All installments shall bear interest until paid at a rate set forth in such ordinance and not to exceed the greater of 9% per annum or 70% of the Prime Commercial Rate in effect at the time of the passage of said ordinance. Interest on assessments shall begin to run from the date of filing of the certificate evidencing the award of the contract for the construction of the improvement, and the interest on each installment shall be payable as follows:
On January 2 next succeeding the filing of the certificate evidencing award of the contract, the interest accrued to that time on all unpaid installments, shall be due and payable and shall be collected with the first installment. Thereafter interest on all unpaid installments, then payable, shall be payable annually, and be due and payable at the same time as the installment maturing in such year, and be collected therewith. In all cases, it shall be the duty of the municipal collector, whenever payment is made on any installment, to collect interest thereon up to the date of such payment, whether the payment be made at or after maturity. Any person may at any time pay the whole assessment against any lot, piece or parcel of land, or any installment thereof, without interest, as hereinafter provided within 20 days after awarding contract or thereafter, with interest to the next interest payment date.
65 ILCS 5/9-3-22