Polk County, Iowa

Polk County is a county located in the U.S. state of Iowa. As of the 2020 census, the population was 492,401, and was estimated to be 516,546 in 2025, making it the most populous county in Iowa. The county seat and the largest city is Des Moines, which is also the capital city of Iowa. Polk County is included in the Des Moines–West Des Moines, IA Metropolitan Statistical Area.