Clay County, Iowa (IA) County population in 2014: 16,515 (66% urban, 34% rural); it was 17,372 in 2000. County owner-occupied with a mortgage or a loan houses and condos in 2010: 3,034. County owner-occupied free and clear houses and condos in 2010: 2,110. County owner-occupied houses and condos in 2000: 5,020.