Illinois Statutes Chapter 625. Vehicles § 5/11-303. The Department to place signs on all State highways

(a) The Department shall place and maintain such traffic-control devices, conforming to its manual and specifications on all highways under its jurisdiction as it shall deem necessary to indicate and to carry out the provisions of this Chapter or to regulate, warn or guide traffic. These traffic control devices shall include temporary stop signs placed as a substitute for missing or damaged permanent stop signs required by the State Manual. Temporary stop signs shall be placed in a manner to provide adequate visibility and legibility, and shall be placed within duration recommendations in the State Manual, unless circumstances require longer placement.

(b) No local authority shall place or maintain any traffic-control device upon any highway under the jurisdiction of the Department except by the latter's permission.

(c) The Department shall erect and maintain guide, warning and direction signs upon highways in cities, towns and villages of which portions or lanes of such highways are under the control and jurisdiction of the Department or for which the Department has maintenance responsibility.

(d) Nothing in this Chapter shall divest the corporate authorities of park districts of power to prohibit or restrict the use of highways under their jurisdiction by certain types or weights of motor vehicles or the power of cities, villages, incorporated towns and park districts to designate highways for one-way traffic or the power of such municipal corporations to erect and maintain appropriate signs respecting such uses.

(e) Nothing in this Section shall prohibit a municipality, township, or county from erecting signs as required under the Illinois Adopt-A-Highway Act. 1