Aurora, Illinois

Where Is Area Code 331?

Area code 331 serves northeastern Illinois in the western suburbs of the Chicago metropolitan area. It is assigned to the same numbering plan area as area code 630. This area includes Aurora and many communities in DuPage, Kane, Will, and Cook counties.

Major cities that use 331 include Aurora, Naperville, Wheaton, Downers Grove, Elmhurst, and Bolingbrook. Other communities in the 331 and 630 service area include Glen Ellyn, Lombard, Oak Brook, West Chicago, and Addison. The area sits west of the city of Chicago and covers a large part of the Fox Valley and nearby suburban corridors.

Notable places in this region include the Fox River in Aurora and Naperville, the Morton Arboretum in Lisle, and Fermilab in Batavia. The service area also includes major suburban business and residential centers along Interstate 88 and Interstate 355. These landmarks and transportation routes reflect the region’s strong suburban growth.

History of Area Code 331

Area code 331 was established on October 7, 2007, as an overlay for area code 630. The Illinois Commerce Commission approved the new code after continued growth increased demand for phone numbers in the western suburbs. Because 331 is an overlay, it did not replace 630 in any city or county.

Area code 630 itself was created in 1996 in a split from area code 708. The 331 overlay was added later so the region could keep adding new numbers without another geographic split. This change reflected long-term population growth, new mobile phone use, and business expansion across suburban Chicago.

Key Facts About Area Code 331

• Area code 331 is in Illinois, and Aurora is one of its best-known cities.
• Area code 331 is an overlay of area code 630, and both codes serve the same region in northeastern Illinois.
• Area code 331 officially entered service on October 7, 2007.
• The 331 and 630 numbering plan area includes parts of DuPage, Kane, Will, and Cook counties.
• Area code 331 is in the Central Time Zone.
• The area code covers major suburban cities such as Aurora, Naperville, Wheaton, Downers Grove, Elmhurst, and Bolingbrook.
• Notable institutions and landmarks in the 331 service area include Fermilab in Batavia, the Morton Arboretum in Lisle, and North Central College in Naperville.
• Ten-digit dialing is required in the 331 overlay area because 331 and 630 serve the same geographic region.

Frequently Asked Questions

What state is area code 331 in?

Area code 331 is in Illinois.

What major cities use area code 331?

Major cities that use area code 331 include Aurora, Naperville, Wheaton, Downers Grove, Elmhurst, and Bolingbrook.

Is area code 331 a toll-free number?

No, area code 331 is a geographic area code for northeastern Illinois.