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

Allegan County is a county in the U.S. state of Michigan. As of the 2020 United States Census, the population was 120,502. The county seat is Allegan. The name was coined by Henry Rowe Schoolcraft to sound like a Native American word.