Adjacent counties

Major highways

National protected areas

• Black Hills National Forest (part)
• Thunder Basin National Grassland (part)

2000 census

As of the 2000 United States Census,^[9] there were 6,644 people, 2,624 households, and 1,868 families in the county. The population density was 3 people per square mile (1.2 people/km²). There were 3,231 housing units at an average density of 1.3 units per square mile (0.50 units/km²). The racial makeup of the county was 95.94% White, 0.12% Black or African American, 1.26% Native American, 0.20% Asian, 0.02% Pacific Islander, 0.93% from other races, and 1.54% from two or more races. 2.06% of the population were Hispanic or Latino of any race. 33.0% were of German, 13.0% English, 8.9% Irish and 7.2% American ancestry.

There were 2,624 households, out of which 31.10% had children under the age of 18 living with them, 60.40% were married couples living together, 7.30% had a female householder with no husband present, and 28.80% were non-families. 25.00% of all households were made up of individuals, and 11.50% had someone living alone who was 65 years of age or older. The average household size was 2.42 and the average family size was 2.88.

The county population contained 24.10% under the age of 18, 7.40% from 18 to 24, 26.30% from 25 to 44, 26.70% from 45 to 64, and 15.60% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 103.10 males. For every 100 females age 18 and over, there were 103.80 males.

The median income for a household in the county was $32,348, and the median income for a family was $40,472. Males had a median income of $34,321 versus $18,640 for females. The per capita income for the county was $17,366. About 6.30% of families and 9.90% of the population were below the poverty line, including 11.30% of those under age 18 and 13.60% of those age 65 or over.

2010 census

As of the 2010 United States Census, there were 7,208 people, 3,021 households, and 1,957 families in the county.^[10] The population density was 3.0 people per square mile (1.2 people/km²). There were 3,533 housing units at an average density of 1.5 units per square mile (0.58 units/km²).^[11] The racial makeup of the county was 95.5% white, 1.3% American Indian, 0.3% black or African American, 0.3% Asian, 0.9% from other races, and 1.7% from two or more races. Those of Hispanic or Latino origin made up 3.0% of the population.^[10] In terms of ancestry, 31.7% were German, 19.3% were Irish, 18.5% were English, 6.6% were Norwegian, 6.1% were Swedish, and 5.6% were American.^[12]

Of the 3,021 households, 26.1% had children under the age of 18 living with them, 53.2% were married couples living together, 6.9% had a female householder with no husband present, 35.2% were non-families, and 29.9% of all households were made up of individuals. The average household size was 2.28 and the average family size was 2.81. The median age was 42.3 years.^[10]

The median income for a household in the county was $53,853 and the median income for a family was $63,438. Males had a median income of $53,095 versus $28,724 for females. The per capita income for the county was $28,463. About 5.8% of families and 7.9% of the population were below the poverty line, including 10.1% of those under age 18 and 10.1% of those age 65 or over.^[13]

City

• Newcastle (county seat)

Town

• Upton

Census-designated places

• Hill View Heights
• Osage

Other places

• Buckhorn^[14]
• Clareton
• Four Corners