70 ILCS 605/11-1
Any drainage district may connect its drains, in the course of natural drainage, or its levees to the drains or levees of another district or to the storm drains or levees of a municipal corporation exercising drainage powers. Any municipal corporation exercising drainage powers may connect its storm drains, in the course of natural drainage, or its levees to the drains or levees of a drainage district. If, by reason of such connection, lands or other property in the district or municipal corporation making the connection receive benefits from work theretofore or thereafter constructed by the other public body, then the district or municipal corporation making the connection shall be liable to the district or municipal corporation conferring the 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 district or municipal corporation making the connection bear to the entire benefits from such work. Whenever the connection is made for the purpose of obtaining an outlet, such connection in itself shall be prima facie evidence of the fact that lands and other property in the district or municipal corporation making the connection are benefited by such work.
Any district may, by a contract in writing with another district or with a municipal corporation exercising drainage powers approved in the manner provided in Sections 11--5, 11--6 and 11--7, obtain the right to connect its drains other than in the course of natural drainage to the drains of the other districts or to the storm drains of the municipal corporation. Any municipal corporation exercising drainage powers may in like manner obtain the right to connect its drains other than in the course of natural drainage to the drains of a drainage district. If a drainage district or municipal corporation exercising drainage powers, by reason of connecting its drains other than in the course of natural drainage, causes damage to any lands or other property by flooding or otherwise, it is liable for such damage to the owners thereof or other persons interested therein and such liability shall not be avoided by the terms of any contract between the two bodies.
70 ILCS 605/11-1