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North American Area code 312 is the State of Illinois telephone area code for the Chicago Loop and surrounding areas of the city of Chicago. It is an enclave area code, similar to area code 213 in Los Angeles and area code 210 in San Antonio, Texas, in that it is completely surrounded by area code 773. It is roughly bounded by North Avenue on the north, Ashland Avenue on the west, and 31st Street on the south, with Lake Michigan to the east. In terms of geographic area covered, the 312 Area Code is one of the smallest area codes in the nation, encompassing only a few square miles.
Area code 312 was one of the original 86 area codes created in 1947, then called "Numbering Plan Areas". With the rotary dialing technology available at the time, care was given to keep the number of "clicks" to a minimum for large cities. For this reason, Chicago was assigned a code with only six clicks.
It originally served almost all of the Chicago metropolitan area. On November 11, 1989, most of the Chicago suburbs were split off as area code 708, with 312 reduced to Chicago itself. 773 was assigned for the remainder of the city outside the downtown area on October 11, 1996; making Chicago one of the few cities in the nation to be split between multiple area codes. Since November 7, 2009, both 312 and 773 are overlaid by 872.
|Illinois area codes: 217, 224, 309, 312, 331, 618, 630, 708, 773, 779, 815, 847, 872|
|West: 773||area code 312 (overlaid by 872)||East: Lake Michigan|
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