65 ILCS 5/9-3-24
All contracts for the construction of any improvement to be paid by special assessment when the expense thereof exceeds $500 shall be let to the lowest responsible bidder after advertisement for bids, as hereinafter provided. However, if aid is received from an agency of the Federal Government, and the application for such aid is approved by an agency of the Federal Government, no such letting of bids is required. If such municipality determines to construct the improvement with the aid from an agency of the Federal Government, then the corporate authorities of any municipality shall make such determination by resolution and file a certified copy of the resolution setting out such determination in the court in which the judgment on confirmation on the assessment has been entered. Thereafter such municipality shall be authorized to proceed with the construction of the improvement without letting a contract therefor, in the manner hereinafter provided.
Within 90 days after the judgment of confirmation of any special assessment has been entered and if there is no appeal perfected from the judgment of confirmation, or the judgment of confirmation as to any property is appealed from, then if the petitioner files in such cause a written election to proceed with the work, notwithstanding such appeal, steps shall be taken to let the contract for such work in the manner hereinafter provided. If the judgment of confirmation is stayed by order of a court, or if the petitioner filed no election to proceed as herein provided, then the steps herein provided for the letting of the contract for such work shall be taken within 15 days after final determination of any stay of the proceedings or of any such appeal, unless the proceedings be abandoned as in this Division 3.
65 ILCS 5/9-3-24