Illinois Statutes Chapter 225. Professions,Occupations and Business Operations § 440/6.03. Spacing

(a) No sign may be erected or maintained in such a manner as to obscure or otherwise physically interfere with an official traffic sign, signal or device or to obstruct or physically interfere with the driver's view of approaching, merging or intersecting traffic within 1000 feet of such sign, signal, device or point of intersecting or merging traffic.

(b) Along interstate highways and expressways no two sign structures on the same side of the highway shall be erected less than 500 feet apart. Along primary highways other than expressways no 2 sign structures on the same side of the highway shall be erected less than 300 feet apart (100 feet inside incorporated municipalities). Except with respect to the repair, rebuilding, or replacement of any sign lawfully erected before January 1, 1993, after the effective date of this amendatory Act of 1992, along primary highways other than expressways, no 2 sign structures on the same side of the highway shall be erected less than 500 feet apart (300 feet inside incorporated municipalities). A sign structure may have one or two facings with a maximum of two signs per facing. Back to back, V-type, and side by side signs shall be treated as single sign structures. Provided, however, that the foregoing spacing between structures requirements shall not apply to structures which are separated or screened by buildings, natural surroundings, or other obstructions in such manner that only one sign facing located within such distance is visible at any one time.

(c) Outside incorporated municipalities, no sign structure may be erected along an interstate highway or expressway adjacent to, or within 500 feet of an interchange, rest area, or weigh station, such 500 feet to be measured along the main-traveled way from the beginning or ending of pavement widening at the exit from or entrance to the main-traveled way.