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Jefferson County, Montana facts for kids

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Jefferson County
Jefferson County Courthouse in Boulder
Map of Montana highlighting Jefferson County
Location within the U.S. state of Montana
Map of the United States highlighting Montana
Montana's location within the U.S.
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Country  United States
State  Montana
Founded February 2, 1865
Named for Thomas Jefferson
Seat Boulder
Largest town Clancy
Area
 • Total 1,659 sq mi (4,300 km2)
 • Land 1,656 sq mi (4,290 km2)
 • Water 2.6 sq mi (7 km2)  0.2%
Population
 (2010)
 • Total 11,406
 • Estimate 
(2020)
12,360
 • Density 7/sq mi (3/km2)
Time zone UTC−7 (Mountain)
 • Summer (DST) UTC−6 (MDT)
Congressional district At-large
  • Montana county number 51

Jefferson County is a county located in the U.S. state of Montana. As of the 2010 United States Census, the population was 11,406. 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 1,659 square miles (4,300 km2), of which 1,656 square miles (4,290 km2) is land and 2.6 square miles (6.7 km2) (0.2%) is water.

Major highways

  • I-90.svg Interstate 90
  • I-15.svg Interstate 15
  • US 12.svg U.S. Highway 12
  • US 287.svg U.S. Highway 287
  • MT-2.svg Montana Highway 2
  • MT-41.svg Montana Highway 41
  • MT-55.svg Montana Highway 55
  • MT-69.svg Montana Highway 69

Adjacent counties

National protected areas

  • Deerlodge National Forest (part)
  • Helena National Forest (part)

Demographics

Historical population
Census Pop.
1870 1,531
1880 2,464 60.9%
1890 6,026 144.6%
1900 5,330 −11.5%
1910 5,601 5.1%
1920 5,203 −7.1%
1930 4,133 −20.6%
1940 4,664 12.8%
1950 4,014 −13.9%
1960 4,297 7.1%
1970 5,238 21.9%
1980 7,029 34.2%
1990 7,939 12.9%
2000 10,049 26.6%
2010 11,406 13.5%
2020 (est.) 12,360 8.4%
US Decennial Census
1790-1960 1900-1990
1990-2000 2010-2020

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 6.9 inhabitants per square mile (2.7/km2). There were 5,055 housing units at an average density of 3.1 per square mile (1.2/km2). 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

Ghost towns

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