Area code
231
231 is a United States area code. Under the North American Numbering Plan it belongs to Michigan, which has 13 area codes in total.
Validate a number in 231
Paste a full number and the tool checks it against the numbering plan. It returns the standard formats, the line type the plan assigns and the area code region.
Digits with or without punctuation work. Numbers outside the US are read with the +country code.
Area code 231 at a glance
NANPA lists 572 central office codes (prefixes) in use in area code 231, held by 42 holders across 99 rate centers.
| Fact | Value |
|---|---|
| In service since | 1999-06-05 |
| Time zone | Eastern (E) |
| Prefixes in use | 572 |
| Pooled prefixes | 382 (67%) |
| Rate centers | 99 |
| Companies holding prefixes | 42 |
| Assignment dates on file | 2001-01-09 to 2026-03-19 (281 prefixes) |
| ZIP codes in its places | 84 |
Rate centers in area code 231
| Rate center | Prefixes | Share |
|---|---|---|
| MUSKEGON | 68 | 12% |
| TRAVERSECY | 53 | 9% |
| PETOSKEY | 22 | 4% |
| CADILLAC | 21 | 4% |
| BIG RAPIDS | 19 | 3% |
| LUDINGTON | 14 | 2% |
| CHEBOYGAN | 13 | 2% |
| MANISTEE | 12 | 2% |
| 91 other rate centers | 350 | 61% |
Who holds the prefixes in 231
Michigan Bell Tel holds the most prefixes, 72 (13%). 67% of the prefixes are pooled, which means their thousands-blocks can belong to different companies.
| Holder | Prefixes | Share |
|---|---|---|
| Michigan Bell Tel | 72 | 13% |
| New Cingular Wireless PCS | 72 | 13% |
| Frontier North | 52 | 9% |
| Onvoy, Llcv | 49 | 9% |
| Interactive Services Network | 43 | 8% |
| Verizon Wireless | 42 | 7% |
| 36 other carriers | 242 | 42% |
A prefix holder is the company a code was assigned to, not necessarily a number's current carrier, because numbers can be ported to another company. Find which carrier a number is on, or browse the prefix holders.
History of area code 231
- 1947-01-01 Area code 616, named as the parent of 231 in the NANPA report, was in service.
- 1999-06-05 Area code 231 went into service.
Area codes nearest to 231
Distance is measured between the centers of the ZIP code places each area code serves, so it is a rough guide.
- 989 about 82 mi
- 616 about 90 mi
- 274 about 126 mi
- 920 about 137 mi
- 269 about 142 mi
ZIP codes in area code 231
84 ZIP codes fall in places that have a rate center in this area code.
| Place | ZIP codes |
|---|---|
| Muskegon, MI | 6 |
| Fremont, MI | 2 |
| Alanson, MI | 1 |
A ZIP code and an area code are unrelated systems. A ZIP code can sit in more than one area code, and an area code spans many ZIP codes.
Complaints on file for 231 numbers
2,130 FCC complaints are on file for 1,569 numbers in 231, most often filed as "Unwanted Calls". These are unverified consumer reports.
| Year of latest complaint | Numbers |
|---|---|
| 2023 | 109 |
| 2024 | 138 |
| 2025 | 137 |
Other area codes in Michigan
Michigan is one state with 13 area codes in the NANPA table. 231 is one of them.
Next to 231 in the numbering table
These are the codes just before and after 231 when all are sorted by number. They are neighbours on the list, not necessarily on the map.
What the area code does and does not tell you
A number that starts with 231 was first assigned in Michigan. That is a fact about where the number began, and it is a useful hint when you check a form entry, for example a billing address in Michigan next to a 231 phone number.
It does not show where the person is today. A number stays with its owner after a move or a change of provider (number portability), and mobile numbers travel with the handset. The area code also cannot tell you whether the line is active, who the carrier is, or whether the number is mobile or fixed: the plan shares those ranges. Read more about the area code, the numbering plan and line type.
Check numbers in bulk with the API
| Product | Credits | Docs |
|---|---|---|
| Phone Numbering-Plan Validation | 1 credit per valid number | API docs |
| Phone Intelligence (carrier and line status) | 1 credit per check (invalid numbers outside the US and Canada are free) | Product page |
Questions about area code 231
Where is area code 231?
NANPA assigns area code 231 to Michigan, United States.
In which state does area code 231 sit?
Michigan. 231 is one of 13 area codes the NANPA table assigns to the state.
Which places does area code 231 cover?
The places with the most ZIP codes among the rate centers in 231 are Muskegon, MI, Fremont, MI and Alanson, MI. The rate center list on this page shows all of them.
Who owns area code 231?
NANPA assigns area codes. Within 231, Michigan Bell Tel holds the most prefixes, 72 prefixes or 13%.
Which time zone does 231 use?
The NANPA NPA report lists the time zone for 231 as Eastern (E).
What year did 231 enter service?
The NANPA NPA report gives an in-service date of 1999-06-05, so 231 has been in use since 1999.
Does area code 231 have an overlay?
The NANPA NPA report lists no other area code in an overlay with 231.
Which area codes are nearest to 231?
The area codes closest to 231, measured between the centers of the ZIP code places they serve, are 989 (about 82 miles), 616 (about 90 miles), 274 (about 126 miles), 920 (about 137 miles) and 269 (about 142 miles).
How many prefixes does area code 231 have?
NANPA's report dated 2026-10-17 lists 572 prefixes in service in 231, spread over 99 rate centers and 42 holders.
Are there complaints about 231 numbers?
The FCC data on file has 2,130 complaints for 1,569 numbers in 231. They are unverified consumer reports. A number with no complaints on file is not proven safe.
Area code assignments: North American Numbering Plan Administrator NPA report, file dated 10/17/2026, retrieved 2026-10-17. Source file. New codes are assigned several times a year. Prefixes, rate centers, holders, time zone, in-service date and overlays: NANPA central office code report dated 2026-10-17 and NPA report dated 2026-10-18. Complaints: FCC consumer complaints open data, fetched 2026-10-17. ZIP code places: Postal code places and coordinates: GeoNames (geonames.org), licensed CC BY 4.0.