Oceana County is a county located in the U.S. state of Michigan. As of the 2020 Census, the population was 26,659. The county seat is Hart. Long known as part of the large Ojibwe territory, the county was founded by European Americans in 1840 and organized in 1855.

Hart is a city and county seat of Oceana County, Michigan. The population was 2,126 at the time of the 2010 census. The city is located within Hart Township, but is politically independent.