The area code 331 is located in Aurora, Illinois.
Area code 331 serves Aurora, Illinois, and the western suburbs of Chicago in the Central Time Zone. It is an overlay of area code 630, created to add numbering capacity across the same region and introduced in 2007 (per NANPA). The 331/630 territory centers on DuPage County and extends into parts of Kane, Kendall, and Will counties, covering busy residential, business, and tech corridors along the I-88 Reagan Memorial Tollway. With the overlay, 10‑digit dialing is required for local calls, and existing 630 numbers did not change when 331 was added.
Area code 331 covers key communities in the western Chicago suburbs, including:
Aurora is a major hub on the Fox River, home to attractions like the historic Paramount Theatre and shopping at Chicago Premium Outlets, with nearby science landmark Fermilab in Batavia also inside the 331/630 service area. The overlay makes it easier to add new phone numbers for homes and businesses without changing existing lines, which helps support steady growth in these suburbs. For anyone seeing a 331 phone number, it most often points to the western suburbs of Chicago, especially Aurora and Naperville, rather than the City of Chicago itself.
Aurora is Illinois’s second-largest city (U.S. Census Bureau).