Geographic Regions and Area Codes

Area code 331 is part of the North American Numbering Plan (NANP) and serves the western suburbs of the Chicago metropolitan area in northeastern Illinois. It covers parts of Cook, DuPage, Kane, Kendall, and Will counties. The primary area code for this region is 331, which overlays with area code 630. Major cities served by area code 331 include Aurora, Naperville, and Bolingbrook. Aurora is the largest city within this area code.