605 ILCS 5/4-203
The Department may, in its discretion and as funds become available for construction and maintenance, add additional highways to the State highway system by laying out new highways or taking over highways from the county highway system, the township and district road system or the municipal street system; but such highways so taken over into the State highway system shall be highways which form a logical part of the State highway system for traffic purposes. Before any such highway is taken over the Department shall notify the proper local officials in writing of its intention to do so and the date when it will assume the maintenance and care of such highway. Whenever any part or portion of any such highway which is situated within the corporate limits of any municipality is hereafter or has heretofore been taken over, the Department shall have exclusive jurisdiction and control over only that part of such highway which the Department has constructed, or which the local authority has constructed and which has been taken over by the Department, and for the maintenance of which the Department is responsible, including the hard-surfaced slab, shoulders and drainage ditches. Whenever any municipality shall construct with a durable hard surface the remaining portion of a street, a part of which has been improved with a durable hard surface by the Department, or taken over by it, then in that case the Department shall have jurisdiction and control over only that portion of the street over which it did construct the durable hard surface or that part which it took over from the municipality.
605 ILCS 5/4-203