Capitalization

Q. I live in the western part of Michigan. My boss thinks we should use West Michigan in a newsletter article, but I think it should be west Michigan. Who is correct? Many thanks.

A. “West Michigan” implies an official political entity like a city, suburb, or state (West Palm Beach, West Chicago, West Virginia). Standard parlance for an unofficial geographical area would be “western Michigan” (capped if the term has acquired a recognized character, like Southern California). However, local usage is also a factor.

[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]