Gallatin County is a county in the U.S. state of Montana. With its county seat in Bozeman, it is the third-most populous county in Montana, with a population of 89,513 in 2010.
According to the US Census Bureau, the county has a total area of 2,632 square miles (6,820 km), of which 2,603 square miles (6,740 km) is land and 29 square miles (75 km) (1.1%) is water. The county attained its present boundaries in 1978, when the former Yellowstone National Park (part) county-equivalent was dissolved and apportioned between Gallatin County and Park County. Gallatin County received 99.155 square miles (256.8 km) of land area and 0.119 square miles (0.3 km) of water area, whereas Park County received 146.229 square miles (378.7 km) of land area and 0.608 square miles (1.6 km) of water area. The geographies transferred are known now as Census Tract 14 in Gallatin County, and as Census Tract 6 in Park County.
As of the 2000 United States Census, there were 67,831 people, 26,323 households, and 16,188 families residing in the county. The population density was 26 people per square mile (10/km²). There were 29,489 housing units at an average density of 11 per square mile (4/km²). The racial makeup of the county was:
1.54% of the population were Hispanic or Latino of any race. 23.7% were of German, 11.2% Irish, 10.4% English, 9.0% Norwegian and 5.5% American ancestry.
In the county households, 29.70% had children under the age of 18 living with them, 51.80% were married couples living together, 6.60% had a female householder with no husband present, and 38.50% were non-families. 24.10% of all households were made up of individuals and 5.70% had someone living alone who was 65 years of age or older. The average household size was 2.46 and the average family size was 2.94.
The county population contained 22.00% under the age of 18, 18.50% from 18 to 24, 30.40% from 25 to 44, 20.60% from 45 to 64, and 8.50% who were 65 years of age or older. The median age was 31 years. For every 100 females there were 108.30 males. For every 100 females age 18 and over, there were 108.70 males.
The median income for a household in the county was $38,120, and the median income for a family was $46,639. Males had a median income of $30,866 versus $21,330 for females. The per capita income for the county was $19,074. About 6.30% of families and 12.80% of the population were below the poverty line, including 10.50% of those under age 18 and 5.60% of those age 65 or over.
As of the 2010 United States Census, there were 89,513 people, 36,550 households, and 21,263 families residing in the county. The population density was 34.4 inhabitants per square mile (13.3/km). There were 42,289 housing units at an average density of 16.2 per square mile (6.3/km). 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.