Major highways

• U.S. Highway 12
• U.S. Highway 87

Adjacent counties

National protected area

• Lake Mason National Wildlife Refuge

2020 census

As of the 2020 census, there were 4,730 people living in the county.^{[citation needed]}

2010 census

As of the 2010 census, there were 4,538 people, 2,046 households, and 1,276 families in the county. The population density was 2.4 inhabitants per square mile (0.93/km²). There were 2,654 housing units at an average density of 1.4 units per square mile (0.54 units/km²). The racial makeup of the county was 96.1% white, 1.3% American Indian, 0.2% black or African American, 0.2% Asian, 0.2% from other races, and 1.9% from two or more races. Those of Hispanic or Latino origin made up 2.6% of the population. In terms of ancestry, 28.1% were German, 16.5% were English, 16.1% were Irish, 7.6% were Norwegian, and 7.0% were American.

Of the 2,046 households, 23.2% had children under the age of 18 living with them, 52.4% were married couples living together, 6.5% had a female householder with no husband present, 37.6% were non-families, and 33.5% of all households were made up of individuals. The average household size was 2.19 and the average family size was 2.78. The median age was 49.1 years.

The median income for a household in the county was $37,033 and the median income for a family was $47,860. Males had a median income of $33,182 versus $25,750 for females. The per capita income for the county was $20,875. About 14.1% of families and 17.8% of the population were below the poverty line, including 28.6% of those under age 18 and 9.6% of those age 65 or over.

City

• Roundup (county seat)

Town

• Melstone

Unincorporated communities

• Delphia^[13]
• Elso^[14]
• Klein
• Queens Point^[15]