There are 10 US Post Offices in Miami County serving a total of 97,655 residents equating to 9,766 residents per post office. It's estimated that approximately 155,868 packages are handled across the 10 county post offices annually. Miami County is a county located in the U.S. state of Ohio. As of the 2010 census, the population was 102,506. Its county seat is Troy. The county is named for an Indian word of disputed meaning. Miami County is part of the Dayton, OH Metropolitan Statistical Area.