M-43 is a state trunkline highway in the southwestern and central parts of the US state of Michigan. The highway runs from South Haven to Webberville along an indirect path through both rural areas and larger cities. The trunkline follows five overall segments: a southeasterly track from South Haven to Oshtemo Township, a northerly path to Plainwell, a southeasterly route to Richland, a northeasterly course to the Hastings area and an easterly route through the Lansing area.

Plainwell is a city in Allegan County in the U.S. state of Michigan. The population was 3,788 at the 2020 census.