On January 13, 1846, the legislative body of the Iowa Territory authorized the creation of twelve counties in the Territory,[5] 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.[6][7] 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.[8]
Geography
According to the United States Census Bureau, the county has a total area of 591.888 square miles (1,532.98km2), of which 572.720 square miles (1,483.34km2) is land and 19.168 square miles (49.64km2) (3.0%) is water.[9] The county is bisected by the Des Moines River.
As of the third quarter of 2024, the median home value in Polk County was $285,410.[15]
As of the 2023 American Community Survey, there are 202,404 estimated households in Polk County with an average of 2.41 persons per household. The county has a median household income of $81,621. Approximately 11.5% of the county's population lives at or below the poverty line. Polk County has an estimated 71.0% employment rate, with 39.5% of the population holding a bachelor's degree or higher and 83.7% holding a high school diploma.[2]
The top five reported ancestries (people were allowed to report up to two ancestries, thus the figures will generally add to more than 100%) were English (85.2%), Spanish (7.8%), Indo-European (1.5%), Asian and Pacific Islander (3.2%), and Other (2.2%).
The median age in the county was 36.8 years.
Polk County, Iowa – racial and ethnic composition Note: the US Census treats Hispanic/Latino as an ethnic category. This table excludes Latinos from the racial categories and assigns them to a separate category. Hispanics/Latinos may be of any race.
As of the 2020 census, there were 492,401 people, 196,891 households, and 121,993 families residing in the county.[21] The population density was 860.5 inhabitants per square mile (332.2/km2). There were 210,184 housing units at an average density of 367.3 per square mile (141.8/km2). The racial makeup of the county was 75.93% White, 7.23% African American, 0.46% Native American, 4.98% Asian, 0.06% Pacific Islander, 3.88% from some other races and 7.45% from two or more races. Hispanic or Latino people of any race were 9.76% of the population.[22]
2010 census
As of the 2010 census, there were 430,640 people, 170,197 households, and _ families residing in the county. The population density was 750.5 inhabitants per square mile (289.8/km2). There were 182,262 housing units at an average density of 317.6 per square mile (122.6/km2). The racial makeup of the county was 84.73% White, 6.00% African American, 0.32% Native American, 3.53% Asian, 0.06% Pacific Islander, 2.93% from some other races and 2.42% from two or more races. Hispanic or Latino people of any race were 7.58% of the population.
2000 census
As of the 2000 census, there were 374,601 people, 149,112 households, and 96,624 families residing in the county. The population density was 658.3 inhabitants per square mile (254.2/km2). There were 156,447 housing units at an average density of 275.0 per square mile (106.2/km2). The racial makeup of the county was 88.34% White, 4.84% African American, 0.27% Native American, 2.63% Asian, 0.06% Pacific Islander, 2.22% from some other races and 1.66% from two or more races. Hispanic or Latino people of any race were 4.40% of the population. 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.
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