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
- 20px Interstate 15
- 20px Interstate 90
- 20px U.S. Highway 12
- 20px U.S. Highway 287
- 20px Montana Highway 2
- 20px Montana Highway 41
- 20px Montana Highway 55
- 20px 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
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