Clay County is a county located in the U.S. state of Iowa. As of the 2020 census, the population was 16,384. Its county seat is Spencer. Its name is in honor of Henry Clay Jr., a colonel who died in action in the Mexican–American War, and son of Henry Clay, famous American statesman from Kentucky. Clay County comprises the Spencer, IA Mi…Clay County is a county located in the U.S. state of Iowa. As of the 2020 census, the population was 16,384. Its county seat is Spencer. Its name is in honor of Henry Clay Jr., a colonel who died in action in the Mexican–American War, and son of Henry Clay, famous American statesman from Kentucky. Clay County comprises the Spencer, IA Micropolitan Statistical Area. Clay County holds the annual Clay County Fair. The first newspaper in Clay County was the Peterson Patriot which started publication in 1880.