225 ILCS 440/3.07
"Sign" means any outdoor sign, display, device, notice, figure painting, drawing, message, placard, poster, billboard, or other thing, which is designated, intended, or used to advertise or inform, and of which any part of the existing or intended advertising or informative contents is or will be visible from any place on the main-traveled way of any portion of an Interstate or primary highway and which is within 660 feet of the nearest edge of the right-of-way of such highway.
"Sign" also means any sign described in paragraph one of this Section which is more than 660 feet from the nearest edge of such highway, outside of an urban area, visible from any place on the main-traveled way of any portion of such highway and erected with the purpose of its message being read from such main-traveled way.
225 ILCS 440/3.07