331
Area code
IL
United States geographic area code, in service since 2007-10-07. Part of the 331/630 overlay complex — ten-digit dialing required.
Statusin service
Introduced2007-10-07
JurisdictionIL, US
Local dialing1+10D
Time zoneCentral
Last verified2026-09-17
Utilization 30.2% of assignable prefixes assigned
As of 09/17/2026
0%239 of ~792 assignable NXX values (200–999 excl. N11)100%
Prefix-level assignment does not equal number-level exhaustion; thousands-block pooling extends capacity. First assignment on record 2007-07-06, most recent 2026-08-14.
Area codes serve rate-center geographies, not municipal boundaries. “IL” identifies the jurisdiction, not an exact city footprint.
Top assignees
Ranked by assigned prefixes · initial assignee ≠ current carrier| Rank | Assignee | Prefixes | Share |
|---|---|---|---|
| 01 | T-MOBILE USA, INC. | 42 | 17.6% |
| 02 | ONVOY, LLC | 39 | 16.3% |
| 03 | CELLCO PARTNERSHIP DBA VERIZON WIRELESS - IL | 33 | 13.8% |
| 04 | NEW CINGULAR WIRELESS PCS, LLC - IL | 26 | 10.9% |
| 05 | FRACTEL, LLC | 18 | 7.5% |
| 06 | BANDWIDTH.COM CLEC, LLC - IL | 11 | 4.6% |
| 07 | TON80 COMMUNICATIONS, LLC | 9 | 3.8% |
| 08 | MULTIPLE OCN LISTING | 9 | 3.8% |
| 09 | LEVEL 3 COMMUNICATIONS, LLC - IL | 6 | 2.5% |
| 10 | 6 | 2.5% |
Important: these are initial assignees from NANPA CO-code records — the carrier a prefix was originally assigned to. Because of number portability, the current serving carrier of any individual number may differ.
Change history
Recorded events for this NPA- 2007-07-06 NPA 331 to Overlay NPA 630 (Illinois)
- 2007-10-07Area code 331 entered service (created from 630).
Planning letters & orders
Primary documents| Date | Document | Subject |
|---|---|---|
| 2007-07-06 | PL-362 ↗ | NPA 331 to Overlay NPA 630 (Illinois) |
| 2006-11-27 | PL-357 ↗ | NPA 331 to Overlay NPA 630 (Illinois) |
| 1999-10-24 | PL-195 ↗ | NPA 872 to Overlay NPAs 312 and 773 (Illinois)NPA 464 to Overlay NPA 708NPA 331 to Overlay NPA 630 |