55 ILCS 5/5-32043
Within 30 days after the final completion of the work, the Committee shall have the costs thereof, including the cost of engineering services certified in writing to the court in which the assessment was confirmed, together with an amount as in this Division is provided for 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 exceeds the cost of the improvement, all of that excess, except the amount required to pay such interest as is provided in this Division shall be abated and the judgment reduced proportionately, so that the property owners shall be credited pro rata upon the respective assessment for the improvement under the direction of the court.
In case the assessment is collectible in the installments, this reduction shall be made so that all installments shall be equal in amount, except that all fractional amounts shall be added to the first installment so as to leave the remaining installments in the aggregate equal in amount and each a multiple of $100. If prior to the entry of the order abating and reducing the assessment, the assessment has been certified for collection and any of the installments of the assessment so certified for collection have become due and payable, the reduction and abatement above referred to shall be made pro rata upon the other installments. The intent and meaning of this is that no property owner shall be required to pay to the collector a greater amount than his proportionate share of the cost of the work and of the interest that may accrue thereon.
55 ILCS 5/5-32043