There are 15 US Post Offices in Hillsdale County serving a total of 46,078 residents equating to 3,072 residents per post office. It's estimated that approximately 73,546 packages are handled across the 15 county post offices annually. Hillsdale County is a county located in the U.S. state of Michigan. As of the 2010 census, the population was 46,688. The county seat is Hillsdale. Hillsdale County comprises the Hillsdale, MI Micropolitan Statistical Area. The Hillsdale County Courthouse was built by Claire Allen, a prominent southern Michigan architect."