Area code 331

Where area code 331 is

NANPA lists 331 as an in-service geographic area code for Illinois, first put into service on October 7, 2007. It is an overlay: 331 and 630 cover the same territory, so neighbors on the same street can have different area codes. It is in the Central time zone. The places with the most assigned exchanges include Aurora, Naperville, Downers Grove, St. Charles, and Lombard. By population, its largest named places are Aurora, Naperville, Downers Grove, Oswego, and Wheaton.

Places served by 331

331 holds 2.5% of the 8,977 central office codes assigned in Illinois, the 13th most of the state's 17 codes. 24 Census places could be matched to rate centers with 331 exchanges; the most populous are Aurora (181,000), Naperville (153,000), Downers Grove (150,000), and Oswego (60,581). Each place page lists the exact prefixes and carriers for that town.

Dialing 331 numbers

According to NANPA's dialing-plan data, local calls within 331 are dialed as 1 plus ten digits and toll calls as 1 plus ten digits. Because local calls need the area code, business cards, signage and website copy should always show the full ten-digit number.

Phone companies in area code 331

25 carriers hold the 224 central office codes assigned in 331. T-mobile USA, INC. has the most, with 42 (19%). 223 of the codes (100%) are pooled, meaning the code holder shares blocks of 1,000 numbers with other carriers instead of using all 10,000 itself. The code holder is not necessarily the carrier serving a given number today, since numbers can be ported between providers.

Rate centers and towns in 331

NANPA assigns each central office code to a rate center, the local calling area that decides whether a call is local or toll. 331 has codes in 24 rate centers. Rate center names in the file are abbreviations; where one matches a Census place, the table links to that city's local-number page.

331 code assignments over time

An area code has 800 possible central office codes that start with 2 through 9, a few of which are reserved (such as N11 service codes and 555). 224 are assigned in 331, 28% of 800. 85 were assigned in 2020 or later.

Using area code 331 for business calls

For $99 a month, Callata puts a team of up to 5 on one plan ($20 for each person after that): up to 3 local numbers, unlimited inbound calls, a pooled allowance of 1,500 outbound US and Canada minutes per user, browser and cell calling, voicemail transcription with urgency triage, recorded calls with AI summaries and business-hours routing, with E911 on every number.

Porting a number you already use in area code 331 is free, and business texting is available once the carrier registration (10DLC) is approved; the registration carries a one-time $49 fee. Which specific numbers are open in a given area code depends on carrier inventory at the time you sign up.

AI agents are optional: an AI receptionist or scheduler can pick up when the team is busy or closed, take a message, send a text or email, or transfer the call. They draw on prepaid AI minutes ($0.25/minute), disclose that they are AI, and outbound AI calls require prior consent and are limited to 8am–9pm.