Major highways

Transit

• Jefferson Lines

Adjacent counties

National protected areas

• Gallatin National Forest (part)
• Yellowstone National Park (part)

2020 census

As of the 2020 census, there were 118,960 people and 46,990 households living in the county.^[10] The population density was 45.2 inhabitants per square mile (17.5/km²). There were 52,835 housing units in the county at an average density of 20.1 per square mile (7.8/km²).^[10] The racial make of the county was 89.0% White, 1.2% Asian, 0.9% American Indian, 0.4% Black of African American, 0.1% Pacific Islander, 1.8% from other races, and 6.6% from two or more races. Those of Hispanic of Latino origin made up 5.0% of the population.^[11] In terms of ancestry, 25.4% were German, 14.8% were Irish, 12.4% were English, 8.8% were Norwegian, 4.6% were Italian, 4.0% were French, 3.5% were Scottish, 2.2% were Polish and 0.3% were Subsaharan African.^[10]

Of the 46,990 households, 48.2% were a Married-couple family household, 23.9% were a "Male householder, no spouse present, family household", and 20.4% were a "Female householder, no spouse present, family household". The averager family size was 2.96 in the county. The median age was 33.1 years old, compared with 40.1 in Montana.^[10]

The median income for a household in the county was $75,418 in the county, significantly higher than the $57,153 median household income in all of Montana. 11.9% of the population was below the poverty line, including 6.9% of those under 18 and 6.5% of those over 65.

2010 census

As of the 2010 census, there were 89,513 people, 36,550 households, and 21,263 families living in the county. The population density was 34.4 inhabitants per square mile (13.3/km²). There were 42,289 housing units at an average density of 16.2 per square mile (6.3/km²). The racial makeup of the county was 95.1% White, 1.1% Asian, 0.9% American Indian, 0.3% Black or African American, 0.1% Pacific Islander, 0.7% from other races, and 1.9% from two or more races. Those of Hispanic or Latino origin made up 2.8% of the population. In terms of ancestry, 32.2% were German, 18.1% were Irish, 14.7% were English, 9.4% were Norwegian, and 3.5% were American.

Of the 36,550 households, 27.8% had children under the age of 18 living with them, 47.8% were married couples living together, 6.6% had a female householder with no husband present, 41.8% were non-families, and 27.3% of all households were made up of individuals. The average household size was 2.36 and the average family size was 2.90. The median age was 32.5 years.

The median income for a household in the county was $50,136 and the median income for a family was $65,029. Males had a median income of $42,245 versus $31,349 for females. The per capita income for the county was $27,423. About 7.4% of families and 13.5% of the population were below the poverty line, including 12.5% of those under age 18 and 8.2% of those age 65 or over.

Cities

• Belgrade
• Bozeman (county seat)
• Three Forks

Towns

• Manhattan
• West Yellowstone

Census-designated places

Unincorporated communities