There are 37 US Post Offices in Hamilton County serving a total of 589,076 residents equating to 15,921 residents per post office. It's estimated that approximately 940,231 packages are handled across the 37 county post offices annually. Hamilton County is a county located in the southwest corner of the U.S. state of Ohio. As of the 2010 census, the population was 802,374. making it the third-most populous county in Ohio. The county seat is Cincinnati. The county is named for the first Secretary of the Treasury, Alexander Hamilton. Hamilton County is part of the Cincinnati-Middletown, OH-KY-IN Metropolitan Statistical Area.