There are 9 US Post Offices in Clinton County serving a total of 45,466 residents equating to 5,052 residents per post office. It's estimated that approximately 72,569 packages are handled across the 9 county post offices annually. Clinton County is a county located in the U.S. state of Ohio. As of the 2010 census, the population was 42,040. The county seat is Wilmington. The county is named for former U.S. Vice President George Clinton. Clinton County comprises the Wilmington, Ohio Micropolitan Statistical Area, which is also included in the Cincinnati-Wilmington-Maysville, OH-KY-IN Combined Statistical Area."