605 ILCS 5/4-406

The Department is authorized to enter into contracts with any municipal corporation, terminable in the discretion of the Department, for the municipal corporation to maintain any State highway, or any part thereof, located within such municipal corporation, such maintenance to be under the supervision of the Department and at the expense of the State.

The Department is authorized to enter into similar contracts with any county for the county to maintain any State highway, or any part thereof, which was originally constructed by the county, such maintenance to be under the supervision of the Department and at the expense of the State.