Jefferson County, Montana
Jefferson County is a county in Montana, United States. As of the 2020 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 United States Census Bureau, the county has a total area of , of which  is land and  (0.2%) is water.

Major highways

  Interstate 15
  Interstate 90
  U.S. Highway 12
  U.S. Highway 287
  Montana Highway 2
  Montana Highway 41
  Montana Highway 55
  Montana Highway 69

Adjacent counties

 Lewis and Clark County - north
 Broadwater County - east
 Gallatin County - southeast
 Madison County - south
 Silver Bow County - west
 Deer Lodge County - west
 Powell County - northwest

National protected areas
 Deerlodge National Forest (part)
 Helena National Forest (part)

Politics

Demographics

2020 census
As of the census of 2020, there were 12,085 people.

2010 census
As of the census of 2010, 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
 Boulder (county seat)
 Whitehall

Census-designated places

 Basin
 Cardwell
 Clancy (includes Alhambra)
 Elkhorn
 Jefferson City
 Montana City
 Rader Creek
 South Hills

Unincorporated communities

 Amazon
 Bernice
 Corbin
 Elk Park
 Homestake
 Leadville
 La Hood Park
 Louisville
 Pappas Place
 Paul Place
 Piedmont
 Pipestone
 Renova

Former communities
 Comet
 Wickes

See also

 List of counties in Montana
 List of lakes in Jefferson County, Montana
 List of mountains in Jefferson County, Montana
 National Register of Historic Places listings in Jefferson County, Montana

References

External links

 

 
Montana counties
1865 establishments in Montana Territory
Helena, Montana micropolitan area
Populated places established in 1865