what area code is 312

Area code 312 is a telephone area code in the North American Numbering Plan for the city of Chicago, including downtown, the Chicago Loop, and its immediate environs. It is completely surrounded by area code 773, which serves the rest of Chicago. Both area codes form an overlay complex with area code 872. The 312 area code is one of the smallest area codes in the nation, encompassing only a few square miles and is an enclave area code, roughly bounded by North Avenue on the north, Western Avenue on the west, and 35th Street on the south, with Lake Michigan to the east. The area code was established in 1947 and is the main area code for the city of Chicago, including downtown Chicago and the Chicago Loop.