65 ILCS 5/11-85-2
The corporate authorities of such municipality and the commissioner of highways in and for such township, in the manner they agree upon, shall procure (1) detailed plans and specifications of the proposed improvement, (2) a detailed estimate of the cost thereof prepared by a competent engineer, showing the total estimated cost of the improvement, and (3) separate estimates from that engineer of the portions thereof within and without the municipality. As soon as the corporate authorities both of the municipality and of the township approve the plans, specifications, and estimates as a basis for the letting of a contract for the improvement, and as soon as the proportions of the cost thereof are agreed upon by the corporate authorities of the municipality and township, they may proceed jointly to let a contract therefor as provided in this section.
This contract shall be let only upon competitive bidding, in the manner provided for the letting of contracts by municipalities for the constructing of local improvements under the provisions of Article 9, except that (1) the advertising for bids for the construction of the proposed improvement shall be authorized and made by the corporate authorities of both the municipality and the township, (2) bids for the construction shall be received by those corporate authorities jointly at the time and place agreed upon and stated in the notice for bids, and (3) no contract shall be let except by the approval of the corporate authorities of both the municipality and the township. All contracts shall be signed and executed by the officials of the municipality and of the township who may be vested generally, by law or ordinance, with the duty of the execution of contracts, for and in behalf of the respective bodies, and all bonds for the performance of a contract shall be made payable to those corporate bodies jointly.
All consents, agreements, and approvals provided for in this Division 85 shall be by writing and when hereby required to be made or given by a municipality, shall be made or given by a resolution of the corporate authorities of the municipality.
65 ILCS 5/11-85-2