815

Area code 815 is a significant telephone area code within the North American Numbering Plan, serving a substantial portion of northern Illinois. Geographic Coverage: Area code 815, along with its overlay area code 779, serves most of northern Illinois, excluding the Chicago and Quad Cities areas. It includes important cities and regions like the Joliet area and some of Chicago’s western and northwestern exurbs. This area code was one of the four original Illinois area codes established in 1947, highlighting its long-standing service in the region​​. Largest City Served and Coverage Area: The largest city within the 815 area code is Rockford. The area code covers a total of 196 cities, including Chicago, Joliet, Rockford, Glenview, and Plainfield. Additionally, it extends over 26 counties, such as Winnebago County, Will County, McHenry County, La Salle County, and Kankakee County, making it an integral part of Illinois's telecommunications network​​​​. Time Zone: Area code 815 is located in the Central Standard Time (CST) zone. Like most areas in the United States, it observes Daylight Saving Time, which involves adjusting the clocks forward in spring and backward in autumn to extend evening daylight during the warmer months of the year​​. In summary, area code 815 is vital for telecommunications in northern Illinois, particularly outside the Chicago and Quad Cities areas. Its establishment in 1947 as one of the original area codes in Illinois and its extensive coverage of numerous cities and counties underscore its importance. The area code's location in the Central Time Zone and adherence to Daylight Saving Time are also key operational aspects.