Clay County is a county located in the U.S. state of Kentucky. As of the 2020 census, the county population was 20,345. Clay County Kentucky is part of the Corbin Kentucky Micropolitan area. Its county seat is Manchester. The county was formed in 1807 and named in honor of Green Clay. Clay was a member of the Virginia and Kentucky State legislatures, first cousin once removed of Henry Clay, U.S. Senator from Kentucky and Secretary of State in the 19th century.