605 ILCS 5/10-205
The plans and specifications for the construction or repair of any such bridge or bridges shall be approved by the county superintendent of highways (or county superintendents of highways, in case two counties of this State are assisting in such construction or repair), and by the Department. The contract for any such work shall be let by the county board (or county boards, in case two counties of this State are assisting in such construction or repair), acting jointly with the corporate authorities of the county, municipality, or other subordinate division of the adjoining state. However, no contract shall be considered as let unless the contractor shall within 15 days after the final award of same, file with the county clerk of such county (or of each such county) a bond, with good and sufficient sureties, in a sum equal to the part of the total cost which that county is to bear, conditioned upon the faithful performance of such contract.
605 ILCS 5/10-205