Clayton County is a county located in the U.S. state of Iowa. As of the 2020 census, the population was 17,043. Its county seat is Elkader. The county was established in 1837 and was named in honor of John M. Clayton, United States Senator from Delaware and later Secretary of State under President Zachary Taylor.

Elkader is a city in Clayton County, Iowa, United States. The population was 1,209 at the time of the 2020 census, down from 1,465 in 2000. It is the county seat of Clayton County. It is the site of Iowa's lowest recorded minimum temperature, −44 °C (−47 °F) on February 3, 1996.