Arthur St. Clair established Adams County on July 10, 1797. He named the county after John Adams, the President of the United States in 1797. It was one of the first four counties created in the Northwest Territory. In 1795, Nathaniel Massie founded Manchester, the first permanent white settlement in Adams County.
Adams County is a rural area, located approximately fifty miles east of Cincinnati along the Ohio River. It consists of 625 square miles of land. West Union is the county seat and it is the largest town in the county. In 2000 the population of West Union was just over 2,900 people. The county averages forty-seven people per square mile. Approximately eighty percent of the residents find employment in service industries. These industries include medical care, utilities, and communications. Just over seven percent of the population is engaged in agriculture, and especially in dairy farming. The average income per person in 1999 was just over sixteen thousand dollars. Adams County is one of the poorest counties in Ohio. Approximately eighteen percent of all residents live in poverty. Many residents describe the county as the "Edge of Appalachia." Politically, the county's residents are predominantly Republican.
Serpent Mound, an Indian earthwork and an Ohio History Connection site, is located in Adams County.