There are 13 US Post Offices in Seneca County serving a total of 62,704 residents equating to 4,823 residents per post office. It's estimated that approximately 100,083 packages are handled across the 13 county post offices annually. Seneca County is a county located in the U.S. state of Ohio. As of the 2010 census, the population was 56,745. Its county seat is Tiffin. The county was created in 1820 and later organized in 1824. It is named for the Seneca Indians. Seneca County comprises the Tiffin, OH Micropolitan Statistical Area, which is also included in the Findlay-Tiffin, OH Combined Statistical Area."