309
Area code
IL
United States geographic area code, in service since 1957-01-01. Part of the 309/861 overlay complex — ten-digit dialing required.
Statusin service
Introduced1957-01-01
JurisdictionIL, US
Local dialing10D
Time zoneCentral
Last verified2026-09-17
Utilization 101% of assignable prefixes assigned
As of 09/17/2026
0%800 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 2001-01-12, most recent 2026-09-09.
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 | FRONTIER NORTH, INC. - IL | 99 | 12.4% |
| 02 | ILLINOIS BELL TEL CO | 83 | 10.4% |
| 03 | ONVOY, LLC | 74 | 9.3% |
| 04 | LEVEL 3 COMMUNICATIONS, LLC - IL | 66 | 8.3% |
| 05 | CELLCO PARTNERSHIP DBA VERIZON WIRELESS - IL | 46 | 5.8% |
| 06 | MEDIACOM TELEPHONY OF ILLINOIS, LLC - IL | 39 | 4.9% |
| 07 | CITIZENS TELECOM CO ILLINOIS-FRONTIER CITIZENS -IL | 35 | 4.4% |
| 08 | T-MOBILE USA, INC. | 34 | 4.3% |
| 09 | NEW CINGULAR WIRELESS PCS, LLC - IL | 34 | 4.3% |
| 10 | BRIGHTSPEED OF ILLINOIS, LLC | 24 | 3% |
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- 2022-01-10 NPA 861 to Overlay NPA 309 (Illinois)
- 1957-01-01Area code 309 entered service.
Planning letters & orders
Primary documents| Date | Document | Subject |
|---|---|---|
| 2022-01-10 | PL-577 ↗ | NPA 861 to Overlay NPA 309 (Illinois) |
| 2021-01-08 | PL-556 ↗ | Transition to 10-digit dialing (for 988 as 3-digit access to National Suicide Prevention Lifeline) – supersedes PL-544 |
| 2020-08-17 | PL-544 ↗ | Transition to 10-digit dialing (for 988 as 3-digit access to National Suicide Prevention Hotline |