Area code 231: Michigan
What is area code 231?
Area code 231 is a US state area code for Michigan, on Eastern Time. It has 572 prefixes in service across 99 rate centers, the largest being Muskegon, Traverse City and Petoskey. NANPA lists no overlay code for it. Local calls there take 7 digits. The code never shows a line is in service.
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See the phone add-onArea code 231 facts
| Location | Michigan, United States |
|---|---|
| Time zone | Eastern Time |
| Overlays | None |
| Split from | 616 |
| In service since | June 5, 1999 |
| Local calls | 7 digits; toll calls 1 + 10 digits |
| Carrier | Not shown. An area code is where a number was issued; numbers port between carriers. Check line type |
In short: 231 is Michigan (Eastern Time). Format checks here are free and run in your browser; the current carrier and line type need a live lookup. Bulk phone number validator · Pro + Phone plan
Local time in area code 231
America/New_York
Prefixes in service
572 of 792 possible
99 rate centers
Which cities and towns use area code 231?
NANPA records each prefix against a rate center, the local billing area a number belongs to, usually named after its main town. These are the 231 rate centers with the most prefixes in service. 87 smaller ones aren't listed.
| Rate center | Prefixes |
|---|---|
| Muskegon | 68 |
| Traverse City | 53 |
| Petoskey | 22 |
| Cadillac | 21 |
| Big Rapids | 19 |
| Ludington | 14 |
| Cheboygan | 13 |
| Manistee | 12 |
| Kalkaska | 10 |
| Fremont | 9 |
| Newaygo | 9 |
| Boyne City | 8 |
Source: NANPA central office code assignments, file dated 10/17/2026. Each prefix holds up to 10,000 numbers.
How do I dial a 231 number?
NANPA's dialling plan for 231: local calls inside the code take 7 digits, toll calls 1 + 10 digits. From another area code, dial 1 first. From abroad, use +1. The examples use 555-0147, from a range reserved for fictional numbers.
| Local call inside 231 | 555-0147 |
|---|---|
| From another US or Canadian area code | 1-231-555-0147 |
| From outside North America | +1 231 555 0147 |
| E.164, for CRMs and SMS tools | +12315550147 |
When did area code 231 start?
Area code 231 went into service on June 5, 1999, split from 616. It has no overlay, so every number in its area still starts with it.
Tools for 231 numbers
- Bulk phone number validator
Format, country and number type for every number in a CSV, with E.164 output.
- Area code lookup
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- Area code time zone
Local time for a list of numbers, with a callable-now flag.
- NPA-NXX lookup
Rate center and state for one prefix, a level below the area code.
- TCPA calling hours checker
Whether it's inside the federal 8 a.m. to 9 p.m. calling window there now.
Next step
A 231 number tells you where it was issued, not what it is now.
Mobiles, landlines and VoIP lines share area codes, and numbers move between carriers. A live line-type and carrier lookup on every number in your list says which is which, and that decides which calling and texting rules apply. It's in the phone add-on.
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Area code 231 questions
- What state is area code 231?
- Area code 231 is in Michigan, United States. Its largest rate centers by number of prefixes are Muskegon, Traverse City, Petoskey, Cadillac and Big Rapids.
- What time zone is area code 231 in?
- Eastern Time.
- Does area code 231 have an overlay?
- Not as of NANPA's file dated 10/16/2026. Every number in its area uses 231.
- When did area code 231 start?
- Area code 231 went into service on June 5, 1999, split from 616.
- Is a 231 number a cell phone or a landline?
- The area code can't tell you. In the US and Canada mobiles, landlines and VoIP lines share area codes and prefixes, and numbers move between carriers and line types. Only a live line-type lookup answers it for one number.
- How many phone numbers does area code 231 have?
- 572 of its 792 possible prefixes are in service, and each prefix holds up to 10,000 numbers. That counts prefixes assigned to carriers, not numbers in use.
- Does a valid format mean a 231 number is in service?
- No. A format check only says the digits fit the North American Numbering Plan and that 231 is an assigned code. It cannot tell whether the number is connected, who answers it or which carrier serves it today, because numbers are reassigned and ported. A live carrier lookup reports the current carrier and line type, but even that is not proof someone answers.
- Can I check a list of 231 numbers for free?
- Yes. Paste them in the list tab above or upload a CSV to the bulk phone number validator: format, E.164, country and the numbering-plan line type are free for every row, with no account. Live carrier and line-type lookups come with Pro + Phone at $49.99/mo (5,000 a month).
Other area codes in Michigan
All Michigan area codes on the area code index.
Sources
Location, overlays, in-service date and dialling plan: NANPA NPA database, file dated 10/16/2026. Prefixes and rate centers: NANPA central office code assignments, 10/17/2026. Time zones mapped to the IANA time zone database. By the SimpleVerifier Team; how we build these pages.