Harrison is a city in western Hamilton County, Ohio, United States. The population was 12,563 at the 2020 census. It is part of the Cincinnati …Harrison is a city in western Hamilton County, Ohio, United States. The population was 12,563 at the 2020 census. It is part of the Cincinnati metropolitan area. Harrison was laid out in 1810, named in honor of William Henry Harrison, a decorated general and state legislator and afterward the ninth president of the United States. It was incorporated in 1850 and became a city in 1981.