Adjacent counties

• Flathead County - north
• Missoula County - east
• Sanders County - west

National protected areas

2020 census

As of the 2020 census, there were 31,134 people living in the county.^{[citation needed]}

2010 census

As of the 2010 census, there were 28,746 people, 11,432 households, and 7,770 families living in the county. The population density was 19.3 inhabitants per square mile (7.5/km²). There were 16,588 housing units at an average density of 11.1 per square mile (4.3/km²). The racial makeup of the county was 69.4% white, 22.0% American Indian, 0.4% Asian, 0.3% black or African American, 0.1% Pacific islander, 0.5% from other races, and 7.3% from two or more races. Those of Hispanic or Latino origin made up 3.5% of the population. In terms of ancestry, 22.3% were German, 11.6% were English, 11.5% were Irish, 6.9% were Norwegian, and 3.8% were American.

Of the 11,432 households, 31.0% had children under the age of 18 living with them, 51.0% were married couples living together, 11.5% had a female householder with no husband present, 32.0% were non-families, and 26.5% of all households were made up of individuals. The average household size was 2.46 and the average family size was 2.97. The median age was 41.3 years.

The median income for a household in the county was $37,274 and the median income for a family was $47,437. Males had a median income of $37,461 versus $26,637 for females. The per capita income for the county was $20,164. About 15.4% of families and 21.6% of the population were below the poverty line, including 33.9% of those under age 18 and 9.3% of those age 65 or over.

Cities

• Polson (county seat)
• Ronan

Town

• St. Ignatius

Census-designated places

Unincorporated communities