Area codes 815 and 779

It also serves the Joliet area and some of Chicago’s western and northwestern suburbs.

When the American Telephone and Telegraph Company (AT&T) created the first nationwide telephone numbering plan for Operator Toll Dialing in 1947, the state of Illinois was divided into four numbering plan areas (NPAs).

815 was assigned to the northern band outside Chicago as one of the 86 original North American area codes.

After September 1956,[1] the 815 numbering plan area was divided roughly in half along a north-westerly to south-easterly running line.

Area code 309 was created by merging the western part of 815, including the Illinois side of the Quad Cities, with the northern portion of area code 217.