70 ILCS 605/11-2

Whenever any work constructed or ordered to be constructed by any drainage district has benefited or will benefit lands outside of that district but within the boundaries of another district or within the boundaries of a municipal corporation exercising drainage powers, the other district or the municipal corporation is liable to the district conferring such benefits for the just proportion of the cost of such work and of the cost of the enlargement, improvement, maintenance, repair and operation thereof based upon the relation which the benefits to the lands in the other district or the municipal corporation bear to the entire benefits from such work.