---
title: "Area code 231: Michigan, United States"
url: "https://lookvalid.com/area-code/231.md"
canonical_url: "https://lookvalid.com/area-code/231"
last_updated: "2026-10-23"
type: "reference"
summary: "Area code 231 serves Michigan, United States. Number formats, numbering rules, a live phone validator and the other codes in Michigan."
---

# Area code 231: Michigan, United States

Area code 231 serves Michigan, United States. Number formats, numbering rules, a live phone validator and the other codes in Michigan.

NANPA lists 572 central office codes (prefixes) in use in area code 231, held by 42 holders across 99 rate centers.
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.
The FCC unwanted-call data has 2,130 complaints on file for 1,569 numbers in 231, most often filed as "Unwanted Calls". These are consumer reports, not findings.

## Facts

- 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

| 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% |

## Carriers

| 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.

## History

- 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.

## Nearest area codes

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).

## ZIP codes

84 ZIP codes fall in places that have a rate center in this area code. The places with the most are Muskegon, MI (6 ZIP codes), Fremont, MI (2 ZIP codes) and Alanson, MI (1 ZIP code). A ZIP code and an area code are unrelated systems, so a ZIP code can sit in more than one area code and an area code spans many ZIP codes.

## Complaints on file

2,130 complaints for 1,569 numbers. Numbers whose latest complaint falls in each year:

- 2023: 109
- 2024: 138
- 2025: 137

## Questions

### 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.

Sources: NANPA central office code report dated 2026-10-17; NANPA NPA report dated 2026-10-18; FCC unwanted-call complaints, data fetched 2026-10-17; ZIP code places from GeoNames (CC BY 4.0).