605 ILCS 5/3-104.1
The Department in cooperation with the municipal corporate authorities or county authorities is authorized to select and designate separate networks of municipal streets to be known as the federal aid urban system of streets and highways in urban areas. The highways included in such networks shall be selected and designated in accordance with the provisions of the Federal Aid Road Act.
Any street or highway included in the federal aid urban system may be constructed jointly at the expense of the federal government and the State of Illinois, or jointly at the expense of the federal government, a municipality or municipalities, or a county or counties, or jointly at the expense of the federal government, the State of Illinois, a municipality or municipalities or a county or counties, in accordance with the provisions of the Federal Aid Road Act.
The authority having jurisdiction over a street or highway prior to its improvement as a federal aid urban project shall be responsible for maintenance, at its own expense. If at any time the Department finds that a street or highway improved as a federal aid project is not being properly maintained by such municipality or county, the Department shall call such fact to the attention of the corporate authorities or county authorities, and if within 90 days after receipt of such notice the street or highway has not been put in a condition of proper maintenance satisfactory to the Department and the Federal Highway Administration, then the Department shall immediately proceed to have such street or highway placed in proper condition of maintenance and charge the costs thereof against the municipality's allotment or the county's allotment of motor fuel tax funds.
605 ILCS 5/3-104.1