Area code 231 is a telephone area code in the North American Numbering Plan (NANP) for the northwestern portion of the Lower Peninsula in the U.S. state of Michigan.

Area code 231 was created in June 1999 by an area code split of area code 616, which had served the entire western half of the Lower Peninsula, extending west from the north-south line aligned with the Mackinac Bridge. 231 was carved out of the northern part. It is centered around the western half of the territory generally defined as Northern Michigan. It also includes Muskegon, which is almost universally counted as part of West Michigan.

The numbering plan area includes the following communities:

• Planning letter 167, which details 231's creation (PDF)
• "Michigan [map] | NANPA". NANPA. Retrieved June 25, 2025.
• Map of Michigan area codes Archived 2008-06-30 at the Wayback Machine at North American Numbering Plan Administration's website
• List of exchanges from AreaCodeDownload.com, 231 Area Code

44°30′N 85°30′W / 44.5°N 85.5°W / 44.5; -85.5