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 southern border, Hillsdale County has the southernmost point in the state. Hillsdale County is conterminous with the Hillsdale, MI Micropolitan Statistical Area. The Hillsdale County Courthouse was designed by Claire Allen, a prominent southern Michigan architect.

Claire Allen was an American architect prominent in southern Michigan in the early twentieth century, and best known for designing several county courthouses. He was considered a "master regional architect".