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 Indiana Territory authorized creation of twelve counties in the Iowa Territory, with general descriptions of their boundaries. 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 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, of which is land and is water.
Iowa Highway 141 – runs east across northern portion of county, through Dawson, Perry, Bouton and Woodward, then southeast to exit into Polk County at Granger
The 2010 census recorded a population of 66,135 in the county, with a population density of. There were 27,260 housing units, of which 25,240 were occupied.
2000 census
As of the census of 2000, there were 40,750 people, 15,584 households, and 11,173 families in the county. The population density was 70 people per square mile. There were 16,529 housing units at an average density of 28 per square mile. The racial makeup of the county was 94.75% White, 0.74% Black or African American, 0.15% Native American, 0.69% Asian, 0.04% Pacific Islander, 2.79% from other races, and 0.84% from two or more races. 5.40% of the population were Hispanic or Latino of any race. Of the 15,584 households 37.20% had children under the age of 18 living with them, 60.60% were married couplesliving 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 60% of the vote nor has a Democrat not won less than 40% since then.
