Area code 779 is an overlay for area code 815, serving northern Illinois outside the Chicago metropolitan area. It was introduced in 2007 due to increasing demand for phone numbers in the region. The 779/815 area includes cities such as Rockford, Joliet, DeKalb, and Kankakee. It spans a mix of urban centers, suburban communities, and rural farmland, reflecting the diversity of northern Illinois. Ten-digit dialing is required throughout the area. While 815 holds historical significance, 779 is commonly used for newer mobile lines and businesses. The dual-code system ensures continuity while supporting regional growth and development.