North American Numbers Source-cited · ownership disclosed
Area code
423
In service
United States · since 1995

Chattanooga / Tri-Cities

Serves a non-contiguous East Tennessee area — Chattanooga and Cleveland in the south, the Tri-Cities and Morristown in the northeast — in an all-services overlay with 729 since 2025.

The essentials Numbering data · NumberResearch · as of 2026-09-18
Place
Chattanooga / Tri-Cities
Type
geographic
Status
in service
In service since
1995
Projected exhaust
2081 Q1

Status, dates and counts are read from NumberResearch (NANPA / CNAC / FCC records). Assignment records show initial assignees, not the carrier serving a number today.

A · Where it is

Where 423 is

East Tennessee in two separate sections divided by area code 865, plus parts of Van Buren and Sequatchie counties in Middle Tennessee..

Communities served wholly or partly by 423:

ChattanoogaClevelandKingsportJohnson CityBristolMorristownGreeneville

Geographically non-contiguous: a southern section (Chattanooga/Cleveland) and a northeastern section (Tri-Cities), separated by 865.

B · Relationships

How it relates to other codes

The codes 423 was split from, spawned, or shares its area with. A split divides the map and changes some numbers; an overlay shares the same ground and changes none — what's the difference?

Split from · 1995 615 Nashville Split from 615 in 1995 as the eastern portion of the state — first new TN area code in 41 years.
Spawned · 1999 865 Knoxville Knoxville and central East Tennessee split off as 865, leaving 423 non-contiguous.
Overlay · 2025 729 Chattanooga / Tri-Cities (overlay) All-services overlay of the same 423 geography.
What's changing. Overlaid by 729 as of 2025; ten-digit dialing mandatory since Aug 5, 2025.
C · History

How 423 got here

1995
Area code 423 created by splitting the eastern portion of 615.
Source: Wikipedia
1999-11-01
Area code 865 split off for Knoxville/central East Tennessee, making 423 non-contiguous.
Source: Wikipedia
2025-08-05
Ten-digit dialing became mandatory for the 423/729 overlay.
Source: Wikipedia
2025-09-05
Official in-service date for area code 729.
Source: Wikipedia
D · Capacity

How full it is

Prefixes assigned
778
Prefixes available
22
Thousands-blocks assigned
3,769

Prefix-assignment counts describe allocation to carriers, not how many individual numbers are in use. Full technical records: NumberResearch ↗.

Compare 423 with another code →
Sources
Wikipedia ↗
Area codes 423 and 729
NumberResearch.org ↗
Live status, dates, assignment counts and exhaust forecast — data as of 2026-09-18 (CC BY 4.0).

Place, relationships and history above are compiled by North American Numbers from the sources listed and last checked 2026-09-18. A check date is not an expert review — see how this is made. Flag an error.