Clay county was formed in 1807. It is located in the Eastern Coal Field region of the state. The elevation in the county ranges from 690 to 2235 feet above sea level. In 2010 the county population was 21,730 in a land area of 469.25 square miles, an average of 46.3 people per square mile.
The county seat is Manchester.
Most of the county is within the Daniel Boone National Forest.