What is what area code is 331?

Area code 331 is a telephone area code in the North American Numbering Plan (NANP) for the state of Illinois, United States. It was established in 2007 to overlay the existing area code 630, which serves the western suburbs of Chicago. Area code 331 covers areas such as Aurora, Naperville, Elgin, Wheaton, and other suburban communities in the Chicagoland area. Residents and businesses in these areas are required to dial the full 10-digit phone number, including the area code, for local calls.