331 Area Code – Aurora, Illinois: Location, Time Zone & History

Western Chicago's suburban belt runs on a mix of corporate offices and civic life, and the numbering plan covering Naperville, Aurora, Wheaton, Downers Grove, and Bolingbrook reflects both sides of that equation. Area code 630 was created on August 3, 1996, in a three-way split of area code 708; by the mid-2000s it needed relief, and 331 was introduced on October 7, 2007, as an all-services overlay rather than a further geographic split, with mandatory ten-digit dialing taking effect the same day.

On the business side, the region hosts Fermi National Accelerator Laboratory in Batavia, a hub for scientific research, alongside established healthcare systems, corporate and regional headquarters, and a strong information technology and telecommunications presence. Higher education institutions round out the employment base. At the same time, the area remains firmly residential and community-oriented: Aurora, served by 630 and 331, is Illinois's second-most populous city after Chicago, with 180,542 residents recorded in the 2020 census.

That combination — research campuses and corporate headquarters set among established suburban communities — gives the 630/331 territory a character distinct from either downtown Chicago or the state's smaller rural areas.