Area Code Overview
Area code 231 is a geographic telephone area code in Michigan that went into service on June 5, 1999. The geographic regions covered by this area code overlay has a population of approximately 667,771.
Overlay and Dialing Rules
- Area Code: 231
- State: Michigan
- Type: General Purpose Code
- In Service Date: June 5, 1999
- Overlay Complex: 231
- Local Dialing Plan: This area does not require you to dial the area code when calling locally.
Estimated Number of Assigned Phone Numbers in Area Code 231
This area code is ranked 206th out of 363 nationwide in estimated assigned phone numbers. Within the state territory it serves, it is ranked 8th out of 12.
Estimated Service-Type Mix of Assigned Phone Numbers in Area Code 231
Estimated Share of Wireless Numbers Originally Assigned to Each Carrier in Area Code 231
Estimated assigned wireless phone numbers: 999,000
Numbers may later be ported to another carrier, but this chart reflects original number assignment, not current subscriber share.
Estimated Share of Wireline and VoIP Numbers Originally Assigned to Each Carrier in Area Code 231
Estimated assigned wireline and VoIP phone numbers: 2,123,000
Other / Unclassified Assigned Numbering in Area Code 231
Estimated assigned other or unclassified phone numbers: 1,237,000
Cities and Towns in Area Code 231
How These Figures Were Built
These figures are estimates based on public phone-number assignment records. They are meant to show the likely mix of assigned phone numbers associated with area code 231, not live customer counts.
Some providers may have assigned phone numbers tied to this area code even if they do not actively market or sell service locally. These figures reflect public number-assignment records, not confirmed local service availability.
They also do not reflect number portability at the individual phone-number level, so some numbers may now be used on a different network or by a different provider than the original assignment records suggest.
Population data and locality matching provided by GeoNames.
Last refreshed: April 15, 2026 6:22 pm