70 ILCS 605/8-15
When a drainage district contains lands lying within a municipal corporation which has constructed drains or levees and which is exercising storm drainage powers in that territory of the same nature as the drainage powers being exercised by the drainage district then all the lands within such municipal corporation and within the drainage district may be detached from the drainage district by the court upon petition of the landowners in the territory sought to be detached, the commissioners of the drainage district or the corporate authorities of the municipal corporation. When any lands are so detached from a drainage district and the drainage system of the drainage district is so situated that it will continue to protect the detached lands from overflow or continue to provide an outlet for the storm drainage of those lands, the municipal corporation shall be liable to the drainage district for its proportionate share of the cost of future construction, repair and maintenance work on the levee or outlet, based upon the benefits to be received by the detached lands.
70 ILCS 605/8-15