On January 13, 1846, the legislative body of the Iowa Territory authorized the creation of twelve counties in the Territory,[4] with general descriptions of their boundaries. On January 17 they further enacted a resolution setting the effective date of the county government for Jasper and Polk Counties as March 1, 1846.[5] Polk County's name referred to United States President James K. Polk, who served from 1845 to 1849.
The first courthouse, a two-story structure, was built in Des Moines in 1846. Rapid settlement and commercial growth in the county soon rendered this building insufficient, so construction of a larger building was initiated in 1858. 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.[6]
Geography
According to the United States Census Bureau, the county has a total area of 592 square miles (1,530 km2), of which 574 square miles (1,490 km2) is land and 18 square miles (47 km2) (3.0%) is water.[7] The county is bisected by the Des Moines River.
U.S. Decennial Census[9] 1790–1960[10] 1900–1990[11] 1990–2000[12] 2010–2020[1]
Population of Polk County from US census data
2020 census
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). 92.55% of the population reported being of one race. 66.18% were non-Hispanic White, 7.23% were Black, 9.76% were Hispanic, 0.46% were Native American, 4.98% were Asian, 0.06% were Native Hawaiian or Pacific Islander and 11.33% were some other race or more than one race. There were 210,184 housing units, of which 196,891 were occupied.
2010 census
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). There were 182,262 housing units, of which 170,197 were occupied.
2000 census
2000 Census Age Pyramid for Polk County
As of the census of 2000, there were 374,601 people, 149,112 households, and 96,624 families in the county. The population density was 658 inhabitants per square mile (254/km2). There were 156,447 housing units at an average density of 275 per square mile (106/km2). The racial makeup of the county was 88.34% White, 4.84% Black or African American, 0.27% Native American, 2.63% Asian, 0.06% Pacific Islander, 2.22% from other races, and 1.66% from two or more races. 4.40% of the population were Hispanic or Latino of any race. 25.9% were of German, 10.6% Irish, 9.0% English and 8.4% American ancestry.
Of the 149,112 households 32.20% had children under the age of 18 living with them, 51.00% were married couples living together, 10.30% had a female householder with no husband present, and 35.20% were non-families. 28.10% of households were one person and 8.60% were one person aged 65 or older. The average household size was 2.45 and the average family size was 3.04.
Age spread: 25.70% under the age of 18, 9.40% from 18 to 24, 32.20% from 25 to 44, 21.50% from 45 to 64, and 11.10% 65 or older. The median age was 34 years. For every 100 females, there were 94.20 males. For every 100 females age 18 and over, there were 90.70 males.
The median household income was $46,116 and the median family income was $56,560. Males had a median income of $37,182 versus $28,000 for females. The per capita income for the county was $23,654. About 5.30% of families and 7.90% of the population were below the poverty line, including 9.70% of those under age 18 and 6.40% of those age 65 or over.
In the first third of the 20th century, Polk County was primarily Republican, backing its candidates in all presidential elections from 1896 to 1932 except for 1912 & 1916. From 1936 to 1980, the county was a swing county, only failing to back the national winner during that period in 1960 & 1968. Starting with the 1984 election, the county has become consistently Democratic like many midsize urban counties, backing the party's candidate in every presidential election from that point forward. Following national trends, suburbs of Des Moines such as Urbandale and Ankeny have changed from Republican strongholds into moderate areas; as Iowa shifted dramatically from competitive to firmly Republican during the Donald Trump era in the mid-to-late 2010s, this is one of the state's few remaining Democratic strongholds.
United States presidential election results for Polk County, Iowa[14]
United States
Iowa
