Generally, it refers to the Grand Rapids-Muskegon-Holland area, and more broadly to most of the region along the Lower Peninsula's Lake Michigan shoreline, but there is no official definition.

In general, "West Michigan" often refers to the area bounded by the cities of Muskegon (in the north), Grand Rapids (in the northeast), Kalamazoo–Battle Creek (in the southeast) and St. Joseph–Benton Harbor (in the southwest).

However, definitions of the boundaries of the region vary widely; in some contexts, the term "West Michigan" is applied only to the counties of Allegan, Kent, Muskegon, and Ottawa, which form the core of the Grand Rapids-Kentwood-Muskegon CSA.

[4] The northern boundary of the region is also poorly defined; the population density, land use, economic and cultural character, and physical geography most often associated with West Michigan fades in northern Muskegon and Kent Counties, however areas as far north as Ludington and White Cloud may be included because of their close economic ties to the cities to the south.

Greenville, in Montcalm County's southwest corner, is closely tied economically with Grand Rapids; however, the northeastern corner, around Vestaburg and Edmore, has historically more closely associated with the cities of Mount Pleasant and Alma, which are almost universally reckoned as part of Central Michigan.