423 Area Code: Chattanooga and East Tennessee Location and Time Zone

Introduction

The 423 area code serves East Tennessee in two separate pieces: a southern section around Chattanooga and Cleveland, and a northern section with Morristown, Greeneville and the Tri-Cities of Kingsport, Johnson City and Bristol. Knoxville's 865 sits between them. Since September 5, 2025, new lines in the same territory can be assigned the overlay code 729.

Most of 423 keeps Eastern Time, but not all of it, so this guide spells out where Central Time applies. It also covers how the code was created, the 2025 switch to ten-digit dialing, and what to check before returning a call from a 423 number.

Where Is the 423 Area Code?

Area code 423 is entirely in Tennessee, and its map is unusual: it covers two regions of East Tennessee that don't touch. The Tennessee Public Utility Commission describes the code as serving two non-contiguous regions, with communities such as Bristol, Chattanooga, Johnson City and Kingsport.

The southern region centers on Chattanooga and Cleveland along the Georgia line and reaches west into the Sequatchie Valley. The northern region covers the upper corner of East Tennessee, taking in Morristown, Greeneville and the Tri-Cities. Between the two lies the Knoxville area, which uses 865.

The code also crosses slightly into Middle Tennessee, where portions of Van Buren and Sequatchie counties use 423. The Virginia half of Bristol is outside the code, since 423 stops at the state line.

How 423 Ended Up in Two Pieces

423 began as a split. In 1995 the eastern part of the 615 area, including Knoxville, Chattanooga and the Tri-Cities, received the new code, while 615 kept Middle Tennessee. For a few years 423 covered almost all of East Tennessee.

Demand from cell phones and pagers used up numbers faster than planned, and on November 1, 1999, Knoxville and most of the central part of East Tennessee moved to the new 865. Instead of splitting three ways, 423 kept both the Chattanooga area and the northeast corner of the state, even though they no longer connect. That's why a Chattanooga number and a Kingsport number share an area code while Knoxville, between them, doesn't.

Cities and Counties in the 423 Area Code

AT&T's area code data lists 24 Tennessee counties in 423: Bledsoe, Bradley, Campbell, Carter, Claiborne, Cocke, Greene, Hamblen, Hamilton, Hancock, Hawkins, Johnson, Marion, McMinn, Meigs, Monroe, Morgan, Polk, Rhea, Scott, Sequatchie, Sullivan, Unicoi and Washington. The table places the largest cities in their counties and sections.

Knoxville, Oak Ridge, Maryville and Sevierville are not in 423; they're on 865. For the full lineup of the state's codes, see the Tennessee area codes page.

423 Area Code Time Zones: Mostly Eastern Time

Most 423 numbers are on Eastern Time, including Chattanooga, Cleveland, Morristown and the Tri-Cities, and carrier summaries often stop there. The federal time zone boundary in southeast Tennessee, however, runs along the western lines of Rhea and Hamilton counties, and 423 reaches past it.

West of that line, Marion, Sequatchie and Bledsoe counties are in the Central Time Zone, one hour behind Chattanooga, and all three are 423 counties. The 423 portions of Van Buren County are west of the line too. In the north, Scott and Morgan counties sit on the Eastern side of the boundary.

Both zones observe daylight saving time, so the one-hour gap holds all year. When you book calls with a 423 contact outside Chattanooga or the Tri-Cities, confirm which side of the line they're on.

423 and 729: One Area, Two Area Codes

In 2023, the 423 area was expected to run out of new numbers in the third quarter of 2025. The Tennessee Public Utility Commission approved an overlay on May 30, 2023: area code 729 serves the same two regions as 423, and nobody's existing number had to change.

Until then, local calls within 423 could still be dialed with seven digits, so the overlay brought a new dialing rule. The carrier notices sent in 2024 listed one schedule, and the commission's 2025 announcements set later dates for the last two steps:

Since August 5, 2025, a local call dialed with only seven digits won't complete. Call prices and local calling areas didn't change, and three-digit numbers still work: 911 and 988, plus 211, 311, 411, 511, 611, 711 and 811 where available. The commission's dialing announcement has the details.

How to Tell If a Call From 423 Is Legitimate

A 729 number may look unfamiliar, but it's a genuine East Tennessee code sharing 423's territory. Neither code says anything about the caller's intentions, though, and a spoofed call can display either one.

• Let unknown calls go to voicemail; a genuine caller can leave a name and a reason.
• Look up the organization's number yourself instead of calling back a number the caller gives you.
• Never share a PIN or one-time passcode, or pay by gift card or wire transfer, because a caller insists.
• Be suspicious of deadlines measured in minutes, such as a warrant, a frozen account or a utility shutoff.

Block repeat callers through your phone's settings or your carrier. File fraud reports at ReportFraud.ftc.gov, and add your number to the National Do Not Call Registry at DoNotCall.gov, where you can also report sales calls that keep coming.

How to Dial a 423 Phone Number

Every local call in 423 and 729 now takes the area code plus the seven-digit number, including calls to numbers in your own area code. What counts as a local call stayed the same when the rule changed.

1. 1Calling someone nearby in 423 or 729: dial the area code, then the seven digits, for example (423) 555-0118.
2. 2Calling a 423 number from another US area code: dial 1, then 423 and the number.
3. 3Calling from abroad: start with the international prefix for the country you're in, then 1 and the full ten-digit number.

Reprogram anything that stored seven-digit numbers before 2025, including alarm and medical monitoring systems, gate entry panels, fax machines, speed dials, call forwarding and voicemail settings, so it dials the full number.

How to Get a 423 Phone Number for Your Business

A 423 number fits a business with customers in Chattanooga, Cleveland or the Tri-Cities, and a 729 number covers the same ground. Because the code spans both regions, one area code is familiar to callers in Chattanooga and in Kingsport alike.

1. 1Check the Tennessee area codes Ringflow offers for 423 or 729 availability.
2. 2Have calls ring on Ringflow's mobile and desktop apps, letting owners and staff answer from anywhere.
3. 3Set up an auto attendant if callers need to reach separate locations, such as a Chattanooga office and a Johnson City office.
4. 4Port an existing 423 line so customers keep the number they already have.

Business texting works on the same number. For customers beyond East Tennessee, browse the full list of US area codes.

Conclusion

The 423 area code covers two separate parts of East Tennessee: Chattanooga and Cleveland in the south, and the Tri-Cities, Morristown and Greeneville in the north, with Knoxville's 865 between them. Since 2025 it has shared that map with 729, and all local calls need ten digits.

Keep the time zone wrinkle in mind: most of 423 is Eastern, but its communities in Marion, Sequatchie and Bledsoe counties keep Central Time. If you want a local East Tennessee number, check the Tennessee codes Ringflow offers and try it free.

Frequently Asked Questions