Adams County is a county in the U.S. state of Ohio. As of the 2020 census, the population was 27,477. Its county seat and largest village is West Union. The county is named after John Adams, the second President of the United States.

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.