Hillsboro Map. Hillsboro is a city in and the county seat of Highland County, Ohio, United States.The population was 6,605 at the 2010 census. Hillsboro is located at 39°12?21?N 83°36?50?W / 39.20583°N 83.61389°W / 39.20583; -83.61389 (39.205764, -83.613764).