[1] It is Iowa's most populous county, and home to over 15% of the state's residents.

The county seat is Des Moines,[2] which is also the capital city of Iowa.

The first courthouse, a two-story structure, was built in Des Moines in 1846.

Due to construction delays and the onset of the Civil War, the structure was not completed until 1866.

The present courthouse was erected in 1906, and in 1962 it was extensively renovated and enlarged.

As of the census of 2020, there were 492,401 people and 207,290 households in the county, with a population density of 833.5383/sq mi (321.8310/km2).

As of the census of 2010, there were 430,640 people and 170,197 households in the county, with a population density of 756.371/sq mi (292.037/km2).

[13] The population ranking of the following table is based on the 2020 census of Polk County.