65 ILCS 5/9-3-28
The contract shall be executed by the contractor and the presiding officer of the corporate authorities and attested by the clerk of such municipality under the official seal of the municipality. Such contractor shall supply a surety bond in the full amount of the contract for the faithful performance thereof. Failure of the contractor to enter into such contract and give such bond within the 20 days hereinabove provided for shall constitute a default and the certified check deposited with his bid shall be deemed forfeited, and the municipality shall again re-advertise for bids. Any contractor who enters into a contract for the construction of the improvement and who fails to complete the same within the time mentioned in the contract, or within such further time as the corporate authorities grant shall be in default and a contract may then be relet for the unfinished portions of such work, in the same manner as provided for advertising for bids in the first instance.
65 ILCS 5/9-3-28