The Dakota Territory's legislature authorized a Burbank County (named for governor John. A. Burbank) in 1872. But in 1874 they renamed it Barnes County in honor of Judge Alanson H. Barnes (1818-1890) who was an associate justice of the Territorial Court. It was finally organized in a meeting at Valley City on January 6, 1879.
As of the census of 2000, there were 11,775 people, 4,884 households, and 3,115 families residing in the county. The population density was 8 people per square mile (3/km²). There were 5,599 housing units at an average density of 4 per square mile (1/km²). The racial makeup of the county was 97.91% White, 0.45% Black or African American, 0.76% Native American, 0.19% Asian, 0.12% from other races, and 0.57% from two or more races. 0.54% of the population were Hispanic or Latino of any race. 40.3% were of German and 34.0% Norwegian ancestry according to Census 2000.
There were 4,884 households out of which 27.40% had children under the age of 18 living with them, 53.90% were married couples living together, 6.80% had a female householder with no husband present, and 36.20% were non-families. 31.50% of all households were made up of individuals and 15.90% had someone living alone who was 65 years of age or older. The average household size was 2.29 and the average family size was 2.89.
In the county the population was spread out with 22.30% under the age of 18, 11.30% from 18 to 24, 23.00% from 25 to 44, 23.60% from 45 to 64, and 19.80% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 96.80 males. For every 100 females age 18 and over, there were 95.40 males.
The median income for a household in the county was $31,166, and the median income for a family was $42,149. Males had a median income of $28,504 versus $18,447 for females. The per capita income for the county was $16,566. About 6.40% of families and 10.80% of the population were below the poverty line, including 10.90% of those under age 18 and 10.90% of those age 65 or over.