65 ILCS 5/9-2-74
At any time after the bids have been received pursuant to the provisions of this Division 2, if it appears to the satisfaction of the board of local improvements that the first assessment is insufficient to pay the contract price or the bonds or vouchers issued or to be issued in payment of the contract price, together with the amount required to pay the accruing interest thereon, the board shall make and file an estimate of the amount of the deficiency. Thereupon a second or supplemental assessment for the estimated deficiency of the cost of the work and interest may be made in the same manner as nearly as may be as in the first assessment, and so on until sufficient money has been realized to pay for the improvement and the interest. It shall be on objection to the supplemental assessment that the prior assessment has been levied, adjudicated, and collected unless it appears that in that prior cause upon proper issue made, it was specially found in terms, that the property objected for would be benefited by the improvement no more than the amount assessed against it in that prior proceedings.
If too large a sum is raised at any time, the excess shall be refunded ratably to those against whom the assessment was made.
But if the estimated deficiency exceeds 10% of the original estimate, no contract shall be awarded until a public hearing has been held on the supplemental proceeding in like manner as in the original proceedings. No more than one supplemental assessment shall be levied to meet any deficiency where the deficiency is caused by the original estimate made by the engineer being insufficient.
Where the improvement is to be constructed with the aid and assistance of any federal agency or other governmental agency after judgment of confirmation if there appears a deficiency in assessments levied in excess of 10% of the original estimate the municipality shall not proceed with the construction of the work until a new hearing has been held upon the levy of a special assessment to make up that deficiency.
However, the petitioner, in case it so elects, may dismiss the petition and vacate the judgment of confirmation at any time after the judgment of confirmation is rendered, and begin new proceedings for the same or a different improvement as provided in Section 9-2-65.
65 ILCS 5/9-2-74