65 ILCS 5/9-3-31
The construction of such improvement in accordance with the provisions of the contract shall be under the supervision of the committee on local improvements, and from time to time, as the work under any contract for the improvement progresses, certificates may be issued by the committee on local improvements to the contractor for work completed and payments may be made to the contractor in amounts not to exceed 85% of the work constructed and completed by vouchers payable either in cash or bonds that may be issued, as in this Division 3 provided, upon completion of the work. All such vouchers shall be signed by the presiding officer of the municipality, attested by the clerk and registered, numbered and countersigned by the treasurer. The treasurer shall keep an accurate register of all such vouchers issued.
65 ILCS 5/9-3-31