Highland County is a county located in the U.S. state of Ohio. As of the 2020 census, the population was 43,317. Its county seat is Hillsboro. The county is named for the topography which is hilly and divides the watersheds of the Little Miami and Scioto Rivers. Highland County was created on May 1, 1805, from land taken from Ross, Adams, and Cle…Highland County is a county located in the U.S. state of Ohio. As of the 2020 census, the population was 43,317. Its county seat is Hillsboro. The county is named for the topography which is hilly and divides the watersheds of the Little Miami and Scioto Rivers. Highland County was created on May 1, 1805, from land taken from Ross, Adams, and Clermont counties.