Area code 815 is a telephone area code for most of northern Illinois outside the Chicago and Quad Cities areas. It also serves many of the outer western, southwestern, and northwestern suburbs of Chicago. However, 815 is largely associated with the Greater Rockford area.
815 was one of the four original Illinois area codes set up in 1947. It was split in 1957, when most of its western portion, including most of the Illinois side of the Quad Cities, was combined with part of the northern portion of area code 217 to form area code 309.[1]
In preparation of an overlay area code (779), all calls from the 815 area needed to be dialed with an area code beginning on February 17, 2007. A month later, the 779 code was activated.