The land that now forms Dallas County was ceded by the Sac and Fox nation to the United States in a treaty signed on October 11, 1842.
On January 13, 1846, the legislative body of the Iowa Territory authorized the creation of twelve counties in the Iowa Territory,[5] with general descriptions of their boundaries.[6] Dallas County's name referred to United States Vice President George M. Dallas, who served from 1845 to 1849.
In 1847 the county residents voted to designate Penoch as the county seat (the name was changed to Adel in 1849). The county's population grew rapidly, with settlers coming to claim homesteads. By 1870, the population had crossed the 12,000 mark.
Geography
According to the United States Census Bureau, the county has a total area of 591.605 square miles (1,532.25km2), of which 588.230 square miles (1,523.51km2) is land and 3.375 square miles (8.74km2) (0.57%) is water.[7] It is the 24th largest county in Iowa by total area.[8]
U.S. Decennial Census[11] 1790–1960[12] 1900–1990[13] 1990–2000[14] 2010–2020[2]
Population of Dallas County from the U.S. Census Data
As of the second quarter of 2025, the median home value in Dallas County was $379,620.[15]
As of the 2024 American Community Survey, there are 46,373 estimated households in Dallas County with an average of 2.47 persons per household. The county has a median household income of $95,334. Approximately 5.7% of the county's population lives at or below the poverty line. Dallas County has an estimated 73.4% employment rate, with 54.1% of the population holding a bachelor's degree or higher and 94.4% holding a high school diploma.[2] There were 48,279 housing units at an average density of 82.08 per square mile (31.7/km2).
The top five reported languages (people were allowed to report up to two languages, thus the figures will generally add to more than 100%) were English (86.0%), Spanish (4.3%), Indo-European (3.2%), Asian and Pacific Islander (3.8%), and Other (2.7%).
The median age in the county was 36.6 years.
Dallas 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 99,678 people, 38,291 households, and 26,000 families residing in the county.[21] The population density was 169.45 inhabitants per square mile (65.4/km2). There were 41,125 housing units at an average density of 69.91 per square mile (27.0/km2). The racial makeup of the county was 83.63% White, 2.71% African American, 0.22% Native American, 5.03% Asian, 0.04% Pacific Islander, 2.56% from some other races and 5.81% from two or more races. Hispanic or Latino people of any race were 6.54% of the population.[22]
2010 census
As of the 2010 census, there were 66,135 people, 25,239 households, and _ families residing in the county. The population density was 112.43 inhabitants per square mile (43.4/km2). There were 27,259 housing units at an average density of 46.34 per square mile (17.9/km2). The racial makeup of the county was 92.19% White, 1.39% African American, 0.19% Native American, 2.51% Asian, 0.06% Pacific Islander, 2.13% from some other races and 1.53% from two or more races. Hispanic or Latino people of any race were 6.14% of the population.
2000 census
As of the 2000 census, there were 40,750 people, 15,584 households, and 11,173 families residing in the county. The population density was 69.28 inhabitants per square mile (26.7/km2). There were 16,529 housing units at an average density of 28.10 per square mile (10.8/km2). The racial makeup of the county was 94.75% White, 0.74% African American, 0.15% Native American, 0.69% Asian, 0.04% Pacific Islander, 2.79% from some other races and 0.84% from two or more races. Hispanic or Latino people of any race were 5.40% of the population.
There were 15,584 households, 37.20% had children under the age of 18 living with them, 60.60% were married couples living together, 8.00% had a female householder with no husband present, and 28.30% were non-families. 23.60% of households were one person and 8.20% were one person aged 65 or older. The average household size was 2.59 and the average family size was 3.08.
The age distribution was 28.20% under the age of 18, 6.90% from 18 to 24, 32.10% from 25 to 44, 21.60% from 45 to 64, and 11.10% 65 or older. The median age was 35 years. For every 100 females, there were 97.70 males. For every 100 females age 18 and over, there were 93.80 males.
The median household income was $48,528 and the median family income was $58,293. Males had a median income of $37,243 versus $27,026 for females. The per capita income for the county was $22,970. About 4.00% of families and 5.60% of the population were below the poverty line, including 6.10% of those under age 18 and 7.10% of those age 65 or over.
Prior to 1932, Dallas County was strongly Republican in presidential elections. From 1932 to 1996, it was a swing county, having a Republican lean until 1960 & a Democratic lean from 1964 to 1996, especially after 1980. Since 2000, it has been consistently Republican, though no Republican presidential candidate has won over 58% of the vote nor has a Democrat won less than 41% since then.
United States presidential election results for Dallas County, Iowa[23]
Meyer, Theodoric. "Two Iowa counties an hour apart show America’s growing political divide: Rural Decatur County has moved sharply red, while suburban Dallas County has shifted the other direction" Washington Post January 12, 2024, online
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