The U.S. state of Illinois is divided into 10 distinct geographic numbering plan areas in the North American Numbering Plan (NANP), which are assigned a total of 17 area codes. When the 86 original North American area codes were established in 1947, all of the Chicago metropolitan area was located in numbering plan area 312, the rest of northern Illinois was 815, central Illinois was 217, and southern Illinois was 618.
In 1954, the 217 and 618 numbering plan areas were slightly remapped, and in 1957, area code 815 was split for the assignment of area code 309 to western central Illinois. No further changes were made for 33 years. Since 2023, all numbering plan areas of the state are overlay complexes, requiring 10-digit dialing statewide.
Area code Yearcreated ParentNPA Overlay Numbering plan area 312 1947 – 312/872 Central city area of Chicago, including the Chicago Loop and the Near North Side 773 1996 312 773/872 Chicago area, exclusive of NPA 312 872 2009 312 312/872 City of Chicago 773 773/872 708 1989 312 708/464 South suburbs and inner west suburbs of Chicago, including the Chicago Southland and most west and south suburbs in Cook County including Melrose Park, Norridge, Oak Park, Oak Lawn, Chicago Heights, and Orland Park. 464 2022 708 630 1996 708 331/630 West suburbs of Chicago in DuPage County and Kane County including Wheaton, Naperville, and Aurora 331 2007 630 847 1996 708 224/847 North and northwest suburbs of Chicago including all of Lake County, part of McHenry County, northern Cook County, and northeastern Kane County. The NPA includes Evanston, Des Plaines, Waukegan, and most of Elgin. 224 2002 847 815 1947 – 779/815 Northern Illinois outside of the immediate Chicago area including Joliet, Kankakee, LaSalle, DeKalb, and Rockford 779 2007 815 217 1947 – 217/447 Central Illinois, including the region running west from the Illinois-Indiana border through Danville, Effingham, Champaign–Urbana, Decatur, Springfield, Quincy until Illinois' western border with Missouri and Iowa 447 2021 217 309 1957 217 309/861 Central-Western Illinois including Bloomington–Normal, Peoria, and all the way west to the Illinois part of the Quad Cities including Moline, and Rock Island 815 861 2023 309618 1947 – 618/730 Southern Illinois, including Carbondale and most of the Metro East region of St. Louis suburbs in Illinois 1954 217 730 2023 618
See also List of North American Numbering Plan area codes
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