70 ILCS 605/11-4
Whenever a drainage district has a claim against another district or against a municipal corporation exercising drainage powers, or a municipal corporation exercising drainage powers has a claim against a drainage district for a portion of the cost of constructing, enlarging, improving, maintaining, repairing or operating any drainage or levee work, the commissioners of the 2 districts or the commissioners and the corporate authorities of the municipal corporation, as the case may be, may enter into a written contract settling and adjusting the claim for benefits and fixing the proportionate share of the cost of future maintenance and repair work and operating expenses to be borne by the benefited district or municipal corporation.
70 ILCS 605/11-4