The area code 815 is located in northern Illinois, except for the Chicago metro area, and serves cities such as Rockford, Joliet, and DeKalb. It was created in 1947 and was divided roughly in half along a north-westerly to south-easterly running line in 1957, assigning area code 309 to its western part, including the Illinois side of the Quad Cities. The new area code was one of the first area codes not serving an entire state, but having the digit 0 in the middle position of the code. It was the only new area code created in Illinois between 1947 and the 1989 creation of area code 708. In preparation of an overlay plan with the new area code 779, all calls from the 815 area needed to be dialed with an area code beginning on February 17, 2009. A month later, area code 779 was activated. Here are some of the main locations covered by the 815 area code:
- Joliet
- Rockford
- Plainfield
- Belvidere
- Freeport
- DeKalb
- Dixon
- Loves Park
- Machesney Park
- Morris
- Ottawa
- Rochelle
- Sterling
- Sycamore
- Woodstock
