Hillsdale County is a county located in the U.S. state of Michigan. As of the 2020 Census, the population was 45,746. The county seat is Hillsdale. Hillsdale County is the only county in Michigan to border both Indiana and Ohio. Due to an angle in the state's border with Ohio, Hillsdale County has the southernmost point in Michigan. Hillsdale County is conterminous with the Hillsdale, MI Micropolitan Statistical Area.