Area code 331 – Illinois
331 has served Illinois since 2007, split from 630. 224 of its 786 number blocks are allocated (28%). No carrier dominates: T-Mobile 18.8%, Onvoy / Inteliquent 17.4%, Verizon 16.5%. It shares its geography with overlay codes 630, so local calls take all ten digits. FTC complaints naming a 331 caller ID totalled 591 in the 33 days to 30 October 2026 (175th of 422 ranked codes).
Who holds 331 number blocks
Share of the 224 assigned NXX blocks (28.5% of the 786 possible), across 25 carriers. This is share of number blocks, not of subscribers.
- T-Mobile19.2%
- Onvoy17.4%
- Verizon16.5%
- Other CLEC / VoIP15.2%
- AT&T14.7%
- Bandwidth4.9%
- Lumen2.7%
- Peerless2.2%
- Charter2.2%
- Comcast1.8%
- Telnyx0.9%
- Windstream0.9%
- Vonage0.9%
- Dish0.4%
Spam complaints naming 331
FTC Do Not Call complaints where the caller ID was a 331 number, 28 Sep – 30 Oct 2026 (33 days). Caller IDs on spam calls are frequently spoofed, so these are complaints about the code, not calls proven to originate in it.
Rate centers in 331
NANPA allocates number blocks to rate centers and records their names abbreviated to ten characters, so these are NANPA's codes rather than place names – CHAMPAURBN is Champaign-Urbana, NWYRCYZN01 is a New York City zone. We show them unchanged instead of guessing at the full names. Showing the largest 5 of 24.
Timeline
- 2007 331 goes into service, split from or overlaid on 630.
More about 331
Separate pages for the questions that need their own answer: what time it is there, what the complaint data says, who holds the number blocks, and how the code compares with the one it shares its area with.
Frequently asked about 331
What state is area code 331?
Illinois. It covers the same area as 331/630.
Is a call from 331 a scam?
Not by itself. 331 drew 591 FTC complaints in the 33 days to 30 October 2026, 175th of 422 ranked codes – mid-pack or lower. Spam callers spoof caller IDs, so the only useful check is the full number.
Which carrier owns 331 numbers?
T-Mobile holds the largest share of assigned number blocks at 18.8%. The rest is spread across 3 other carriers. This is share of number blocks, not of subscribers – people keep their numbers when they switch carriers.
Do I need to dial 10 digits in 331?
NANPA records the local dialing plan for 331 as “1+10D”.
Sources and verification
- NANPA – NPA Database (npa_report.csv), file date 11/01/2026, retrieved Nov 1, 2026
- NANPA – CO Code Assignment Records, All States (utilized), file updated 11/01/2026, retrieved Nov 1, 2026
- FTC – Do Not Call Reported Calls Data, 25 daily files 28 Sep – 30 Oct 2026, retrieved Nov 1, 2026
NANPA dialing note for this code: “1+10D”. Reviewed by the data desk. Spotted an error? Request a correction.