JEFFERSON County, MT

Jefferson County is a county in Montana, United States. As of the 2020 United States Census, the population was 12,085. Its county seat is Boulder. The county was created in 1865 and named for President Thomas Jefferson.

Jefferson County is part of the Helena, MT Micropolitan Statistical Area.

Geography

According to the U.S. Census Bureau, the county has a total area of , of which is land and (0.2%) is water.

Major highways

Adjacent counties

National protected areas

Politics

Demographics

2000 census

As of the 2000 United States Census, there were 10,049 people, 3,747 households, and 2,847 families in the county. The population density was 6 people per square mile (2/km²). There were 4,199 housing units at an average density of 2 per square mile (1/km²). The racial makeup of the county was 96.07% White, 0.14% Black or African American, 1.26% Native American, 0.42% Asian, 0.07% Pacific Islander, 0.38% from other races, and 1.66% from two or more races. 1.48% of the population were Hispanic or Latino of any race. 22.9% were of German, 13.1% English, 12.9% Irish, 7.9% Norwegian and 5.3% American ancestry.

There were 3,747 households, out of which 35.60% had children under the age of 18 living with them, 67.10% were married couples living together, 5.90% had a female householder with no husband present, and 24.00% were non-families. 20.20% of all households were made up of individuals, and 7.30% had someone living alone who was 65 years of age or older. The average household size was 2.62 and the average family size was 3.03.

The county population contained 27.80% under the age of 18, 5.20% from 18 to 24, 26.80% from 25 to 44, 29.90% from 45 to 64, and 10.30% who were 65 years of age or older. The median age was 40 years. For every 100 females, there were 100.80 males. For every 100 females age 18 and over, there were 100.40 males.

The median income for a household in the county was $41,506, and the median income for a family was $48,912. Males had a median income of $34,753 versus $25,011 for females. The per capita income for the county was $18,250. About 6.70% of families and 9.00% of the population were below the poverty line, including 10.40% of those under age 18 and 9.60% of those age 65 or over.

2010 census

As of the 2010 United States Census, there were 11,406 people, 4,512 households, and 3,301 families residing in the county. The population density was . There were 5,055 housing units at an average density of . The racial makeup of the county was 95.5% white, 1.4% American Indian, 0.4% Asian, 0.1% black or African American, 0.4% from other races, and 2.2% from two or more races. Those of Hispanic or Latino origin made up 2.0% of the population. In terms of ancestry, 31.3% were German, 19.1% were Irish, 17.2% were English, 10.8% were Norwegian, and 4.2% were American.

Of the 4,512 households, 28.8% had children under the age of 18 living with them, 63.7% were married couples living together, 5.4% had a female householder with no husband present, 26.8% were non-families, and 22.6% of all households were made up of individuals. The average household size was 2.48 and the average family size was 2.90. The median age was 46.2 years.

The median income for a household in the county was $56,695 and the median income for a family was $67,195. Males had a median income of $50,978 versus $34,148 for females. The per capita income for the county was $26,437. About 2.7% of families and 12.8% of the population were below the poverty line, including 5.1% of those under age 18 and 8.6% of those age 65 or over.

Communities

Towns

Census-designated places

Unincorporated communities

Former communities