70 ILCS 2805/86
Except as otherwise provided in Section 9-2-117 of the Illinois Municipal Code, as now or hereafter amended, within 30 days after the final completion and acceptance of the work by the committee as provided in Section 22a.47, the committee of local improvements shall have the cost thereof, including the cost of engineering services, certified in writing to the court in which the assessment was confirmed, together with an amount estimated by the committee to be required to pay the accruing interest on bonds or vouchers issued to anticipate collection. Thereupon, if the total amount assessed for the improvement upon the public and private property exceeds the cost of the improvement, all of that excess, except the amount required to pay such interest as is provided for in this Act, shall be abated and the judgment reduced by applying all of the excess first to the abatement and reduction of the amount assessed against the district for public benefit and the remaining excess, if any, to the abatement and reduction of the amount assessed against the private property to be benefited by the improvement, which abatement of the assessment against benefited property shall be credited pro rata upon the respective assessments for the improvement under the direction of the court. In case the assessment is collectible in installments, this reduction shall be made by reducing the amount of the last installment or installments.
70 ILCS 2805/86