55 ILCS 5/5-13001

In addition to the existing power and to the end that adequate safety may be secured and the congestion of public roads, streets, traffic-ways, drives and parkways may be lessened or avoided, the county board of each county is authorized and empowered to establish, regulate and limit the building or set-back lines on or along any road, street, traffic-way, drive or parkway in the county outside the corporate limits of any city, village or incorporated town, as may be deemed best suited to carry out the provisions of this Division. The powers given by this Division shall not be exercised so as to deprive the owner of any existing property of its use or maintenance for the purpose to which it is then lawfully devoted.