Reported (312) XXX-XXXX phone numbers lookup

Area Code 312 History and Coverage

312 was established in 1947 as one of Illinois' first area codes under the North American Numbering Plan system. Illinois originally had the following area codes: 217, 312, and 618, where 312 covered a vast northern region of the state. The first territory of the area code went far beyond today's tight borders, encompassing metropolitan suburbs, as well as northern communities of Illinois.

With increasing need in telephone numbers, the original territory was shrunk via geographic splits. In 1957, area code 815 was established from the territory of 312 and took much of the northern and western parts of Illinois away from the metropolitan area. In 1989, area code 708 was established in order to cover many suburbs of Cook County, which significantly reduced the territory of 312.

The last split took place in 1996 when area code 773 split off from 312 and got the majority of territory of Chicago except the inner small territory of 312. In 2009, area code 872 was introduced as an overlay for the regions covered by 312 and 773 area codes. Overlay does not rezone the current geographic boundaries unlike geographic split. Such changes have segregated the needs in numbering of the suburbs from the inner zone and added capacity in the city. The current area of 312 has been limited to the urban center of Cook County.