[3] Over two-thirds (67.7%) of the county's land lies within the Flathead Indian Reservation.

[citation needed] As of the 2010 census, there were 28,746 people, 11,432 households, and 7,770 families living in the county.

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.

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.