Hillsdale is the largest city, and county seat, of Hillsdale County, in the U.S. state of Michigan. The population was 8,036, at the 2020 censu…Hillsdale is the largest city, and county seat, of Hillsdale County, in the U.S. state of Michigan. The population was 8,036, at the 2020 census. The city is the home of Hillsdale College, a private liberal arts college.