In the Nebraska license plate system, Dakota County is represented by the prefix 70 (it had the seventieth-largest number of vehicles registered in the county when the license plate system was established in 1922).
1860 - 819 1870 - 2,040 1880 - 3,213 1890 - 5,386 1900 - 6,286 1910 - 6,564 1920 - 7,694 1930 - 9,505 1940 - 9,836 1950 - 10,401 1960 - 12,168 1970 - 13,137 1980 - 16,573 1990 - 16,742 2000 - 20,253
As of the census of 2000, there were 20,253 people, 7,095 households, and 5,087 families residing in the county. The population density was 77 people per square mile (30/km²). There were 7,528 housing units at an average density of 28 per square mile (11/km²). The racial makeup of the county was 78.84% White, 0.62% Black or African American, 1.86% Native American, 3.08% Asian, 0.06% Pacific Islander, 12.91% from other races, and 2.62% from two or more races. 22.62% of the population were Hispanic or Latino of any race. 28.0% were of German and 10.5% Irish ancestry according to Census 2000.
There were 7,095 households out of which 39.90% had children under the age of 18 living with them, 54.60% were married couples living together, 11.90% had a female householder with no husband present, and 28.30% were non-families. 22.90% of all households were made up of individuals and 9.00% had someone living alone who was 65 years of age or older. The average household size was 2.81 and the average family size was 3.30.
In the county the population was spread out with 30.50% under the age of 18, 10.10% from 18 to 24, 29.40% from 25 to 44, 20.10% from 45 to 64, and 9.90% who were 65 years of age or older. The median age was 31 years. For every 100 females there were 99.70 males. For every 100 females age 18 and over, there were 97.10 males.
The median income for a household in the county was $38,834, and the median income for a family was $43,702. Males had a median income of $28,341 versus $22,035 for females. The per capita income for the county was $16,125. About 9.20% of families and 11.40% of the population were below the poverty line, including 14.60% of those under age 18 and 8.60% of those age 65 or over.