Major highways

• Interstate 90
• U.S. Highway 10 (Former)
• Montana Highway 78

Adjacent counties

National protected areas

• Custer National Forest (part)
• Grass Lake National Wildlife Refuge
• Hailstone National Wildlife Refuge

2020 census

As of the 2020 census, there were 8,963 people living in the county.^{[citation needed]}

2010 census

As of the 2010 census, there were 9,117 people, 3,796 households, and 2,657 families in the county. The population density was 5.1 inhabitants per square mile (2.0/km²). There were 4,803 housing units at an average density of 2.7 units per square mile (1.0 units/km²). The racial makeup of the county was 96.8% white, 0.8% American Indian, 0.3% Asian, 0.1% black or African American, 0.4% from other races, and 1.6% from two or more races. Those of Hispanic or Latino origin made up 2.3% of the population. In terms of ancestry, 34.7% were German, 14.1% were Irish, 14.0% were English, 10.8% were Norwegian, and 6.9% were American.

Of the 3,796 households, 28.9% had children under the age of 18 living with them, 60.6% were married couples living together, 6.0% had a female householder with no husband present, 30.0% were non-families, and 25.8% of all households were made up of individuals. The average household size was 2.37 and the average family size was 2.84. The median age was 45.7 years.

The median income for a household in the county was $57,227 and the median income for a family was $65,438. Males had a median income of $51,830 versus $26,909 for females. The per capita income for the county was $27,168. About 6.0% of families and 9.5% of the population were below the poverty line, including 17.9% of those under age 18 and 7.2% of those age 65 or over.

Town

• Columbus (county seat)

Census-designated places

• Absarokee
• Fishtail
• Nye
• Park City
• Rapelje
• Reed Point

Unincorporated communities

Ghost towns

• Limestone
• Springtime
• Wheat Basin