Area Code 312 History:
Area code 312 was put into service. In 1989 Area code 312 was split to form area code 708. In 1996 area code 312 was split again to form area code 773. In 2009 area code 312 was overlaid with area code 872.
Counties in Illinois within area code 312 include:
Major cities or places in Illinois within area code 312 include:
Chicago originally utilized area code 312 which was one of the original area codes assigned to Illinois in 1947. In 1996 area code 312 was split to form area code 773. Area code 312 now serves the downtown area, or inside "The Loop" and area code 773 serves the remainder of the city. On November 7, 2009 area code 872 was put into service. Area code 872 is an overlay of of both 312 and 773.