331 area code
Aurora area, Central Time.Area code 331 covers Aurora, Naperville, Downers Grove and 22 more places in Illinois, on Central Time. 630 covers the same area.
Right now in Aurora
Central Time (CST, UTC-6; CDT, UTC-5 in summer)
Calling hours: Every day, 8 AM to 9 PM (the federal rule)
Small talk
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Where 331 numbers come from
Numbers are issued by rate center, a billing area named for its main town. 331 has 25. Each one's share is how many 331 numbers start there. Its biggest metro area is Chicago-Naperville-Elgin, IL-IN.
- Aurora20%
- Naperville15%
- Downers Grove9%
- St. Charles8%
- Lombard6%
- Elmhurst5%
- Lemont5%
- West Chicago4%
- Bartlett4%
- Wheaton3%
- Geneva3%
- Oswego3%
Also: Hinsdale, Sugar Grove, Yorkville, Itasca, Glen Ellyn, Elburn, Batavia, Warrenville, Big Rock, Kaneville, Plano, Roselle + 1 more
Share of exchanges (blocks of 10,000 numbers). Source: NANPA rate center and exchange reports, November 10, 2026
When can you call a 331 number?
Sales calls to homes and cell phones have legal hours, set by the federal rule. Hold every 331 number to them, since you can't tell a work line from a personal cell.
What applies to 331Every day, 8 AM to 9 PM
- Federal (TCPA and FTC rule)Every day, 8 AM to 9 PMCalls to residential and mobile numbers. Most calls to businesses are exempt from the FTC's rule.47 CFR 64.1200(c)(1); 16 CFR 310.4(c) (opens in a new tab)
Local time comes from the area code, not from where the person is today. Mobiles keep their number when they move. Calling hours here are a guide, not legal advice. Every state's calling hours, with sources
331 and 630
331 went into service on October 7, 2007. 331 and 630 cover the same area, so new numbers can get either code and neighbors can have different area codes. 331 holds 25% of the area's exchanges; 630 holds the most. Local calls take all 10 digits.
- 1996630 overlay
- 2007331 starts
Source: NANPA area code database
Calling a list of 331 numbers?
Paste it into the free phone number validator. It checks every number, finds each one's time zone and sorts the list by who you can call right now.
331 area code FAQ
What area code is 331?
331 is an Illinois area code for Aurora, Naperville, Downers Grove, St. Charles and 21 more places.
What time zone is the 331 area code in?
Central Time (CST, UTC-6; CDT, UTC-5 in summer).
Is 630 the same as 331?
Same area, different code. 331 and 630 cover the same area (an overlay), so new numbers can get any of them and local calls take all 10 digits.
What are the calling hours for 331 numbers?
Every day, 8 AM to 9 PM, local time, under the federal rule.
When did the 331 area code start?
On October 7, 2007.
Calling 331 numbers? Reach more of them.
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