Major highways

• Montana Highway 5
• Montana Highway 16

Adjacent counties and rural municipalities

National protected area

• Medicine Lake National Wildlife Refuge (part)

2020 census

As of the 2020 census, there were 3,539 people living in the county.^{[citation needed]}

2010 census

As of the 2010 census, there were 3,384 people, 1,587 households, and 944 families living in the county. The population density was 2.0 inhabitants per square mile (0.77/km²). There were 2,089 housing units at an average density of 1.2 units per square mile (0.46 units/km²). The racial makeup of the county was 95.4% white, 1.7% American Indian, 0.4% Asian, 0.2% black or African American, 0.3% from other races, and 2.0% from two or more races. Those of Hispanic or Latino origin made up 1.5% of the population. In terms of ancestry, 33.8% were Norwegian, 26.0% were German, 12.0% were Danish, 11.6% were Irish, 5.5% were Swedish, 5.3% were English, and 5.0% were American.

Of the 1,587 households, 21.3% had children under the age of 18 living with them, 49.5% were married couples living together, 5.7% had a female householder with no husband present, 40.5% were non-families, and 37.1% of all households were made up of individuals. The average household size was 2.08 and the average family size was 2.70. The median age was 50.3 years.

The median income for a household in the county was $39,578 and the median income for a family was $55,313. Males had a median income of $46,932 versus $22,107 for females. The per capita income for the county was $26,537. About 6.4% of families and 14.5% of the population were below the poverty line, including 8.8% of those under age 18 and 10.4% of those age 65 or over.

City

• Plentywood (county seat)

Towns

• Medicine Lake
• Outlook
• Westby

Unincorporated communities

Former towns

• Dooley
• Archer