Jefferson County is a county in Montana, United States, straddling the Continental Divide corridor between Helena and Butte. It had a population of 12,085 at the 2020 census and covers 1,659 square miles (4,300 km2) centred near 46°11′N 112°07′W.
Boulder is the county seat, and its postal code is 59632. The county has 2 incorporated towns, 7 census-designated places and a long list of unincorporated communities and former mining camps. Jefferson County observes Mountain Time and is part of the Helena, MT Micropolitan Statistical Area.
Towns & Villages in Jefferson County
Only Boulder and Whitehall are incorporated towns; Clancy, Basin, Cardwell, Elkhorn, Jefferson City, Montana City, Rader Creek and South Hills are Census Bureau-designated places (CDPs) with no town government of their own. The rest of the list below is unincorporated communities and historic mining-camp names carried on U.S. Geological Survey maps — several, such as Comet, Elkhorn, Wickes and Leadville, are now ghost towns or near-ghost towns left over from the county’s silver boom.
| Place | Type | Pop. | ZIP |
|---|---|---|---|
| Boulder | City · seat | — | 59632 |
| Whitehall | Town | — | 59759 |
| Clancy | CDP | — | 59634 |
| Basin | CDP | — | 59631 |
| Cardwell | CDP | — | 59721 |
| Elkhorn | CDP | — | — |
| Jefferson City | CDP | — | 59638 |
| Montana City | CDP | — | — |
| Rader Creek | CDP | — | — |
| South Hills | CDP | — | — |
| Alhambra | Unincorp. | — | — |
| Amazon | Unincorp. | — | — |
| Bernice | Unincorp. | — | — |
| Blazing Place | Unincorp. | — | — |
| Cedric | Unincorp. | — | — |
| Clasoil | Unincorp. | — | — |
| Comet | Unincorp. | — | — |
| Corbin | Unincorp. | — | — |
| Donald | Unincorp. | — | — |
| Elk Park | Unincorp. | — | — |
| Fuller | Unincorp. | — | — |
| Homestake | Unincorp. | — | — |
| Kyle | Unincorp. | — | — |
| La Casa Trailer Park | Unincorp. | — | — |
| La Hood Park | Unincorp. | — | — |
| Leadville | Unincorp. | — | — |
| Louisville | Unincorp. | — | — |
| Mountain Valley Trailer Court | Unincorp. | — | — |
| Pappas Place | Unincorp. | — | — |
| Paul Place | Unincorp. | — | — |
| Piedmont | Unincorp. | — | — |
| Pipestone | Unincorp. | — | — |
| Pipestone Hot Springs | Unincorp. | — | — |
| Portal | Unincorp. | — | — |
| Queen | Unincorp. | — | — |
| Renova | Unincorp. | — | — |
| Rice Motel and Trailer Court | Unincorp. | — | — |
| Rieder | Unincorp. | — | — |
| Sunlight | Unincorp. | — | — |
| Sunset Trailer Court | Unincorp. | — | — |
| Tippet Place | Unincorp. | — | — |
| Trask | Unincorp. | — | — |
| Vendome | Unincorp. | — | — |
| Welch | Unincorp. | — | — |
| Wickes | Unincorp. | — | — |
| Woodville | Unincorp. | — | — |
Elkhorn is listed both as a modern CDP boundary drawn by the Census Bureau and as the historic silver-mining town whose false-front buildings survive at Elkhorn Ghost Town State Park — the two names refer to the same place, not a duplicate.
ZIP Codes
- 59632 — Boulder (also serves Basin-area routes)
- 59634 — Clancy
- 59759 — Whitehall
- 59638 — Jefferson City (PO Box only)
- 59631 — Basin (PO Box only)
- 59721 — Cardwell
Smaller communities such as Montana City, Elkhorn and Rader Creek do not have their own ZIP code and use a neighboring town’s address.
Geography
Jefferson County sits along the Continental Divide in southwestern Montana, where the Boulder and Jefferson Rivers cut through the Elkhorn and Boulder mountain ranges. The county contains portions of both Deerlodge National Forest and Helena National Forest, and its terrain ranges from the irrigated Jefferson River valley in the south to the timbered peaks around Elkhorn in the northeast.
Jefferson County borders Lewis and Clark County to the north, Broadwater County to the east, Gallatin County to the southeast, Madison County to the south, Silver Bow County and Deer Lodge County to the west, and Powell County to the northwest.
Demographics
The county’s population was 12,085 at the 2020 census, spread across 1,656 square miles of land for a density of roughly 7 people per square mile — among the least densely settled counties on the Helena-Butte corridor. Clancy is the largest community, followed by Boulder, the county seat and largest incorporated town. For comparison, the Montana state median household income was $70,804 (2023 ACS).
Economy & Local Life
Jefferson County’s economy has shifted from the hard-rock silver and gold mining that built towns like Wickes, Comet and Elkhorn in the 1880s to ranching, timber and commuting: Clancy, Montana City and Jefferson City lie within daily commuting distance of Helena, while Whitehall and Cardwell serve the ranching country along the Jefferson River. Boulder Hot Springs, a historic mineral-spring resort south of Boulder, and Elkhorn Ghost Town State Park are the county’s best-known visitor attractions.
History
Jefferson County was organized in 1865, one of Montana Territory’s original counties, and named for President Thomas Jefferson. Its early economy centred on the silver and gold strikes at Elkhorn, Comet and Wickes; Elkhorn’s mines produced tens of millions of dollars in silver before the 1893 silver crash emptied the town, leaving the false-front buildings that still stand today. Boulder was chosen as the county seat for its position along the wagon road between Helena and Butte.
Getting There
Interstate 15 runs north-south through the county past Boulder and Basin, and Interstate 90 clips the southern edge near Whitehall and Cardwell; U.S. Highways 12 and 287 and Montana Highways 2, 41, 55 and 69 connect the smaller communities.
- Helena — 30 miles north
- Butte — 30 miles southwest
- Bozeman — 80 miles east
- Three Forks — 25 miles southeast
The nearest commercial airport is Helena Regional Airport (HLN).
Frequently Asked Questions
Where is Jefferson County, Montana?
It lies in southwestern Montana along the Continental Divide, between Helena and Butte, and is part of the Helena, MT Micropolitan Statistical Area.
What is the population of Jefferson County?
Jefferson County had a population of 12,085 at the 2020 census.
How big is Jefferson County?
The county covers 1,659 square miles (4,300 km2), of which 1,656 square miles are land.
What is the county seat of Jefferson County?
Boulder is the county seat.
How many towns are in Jefferson County?
Only two places are incorporated — Boulder and Whitehall — alongside seven census-designated places and dozens of unincorporated communities.
What ZIP codes are in Jefferson County?
The main ZIP codes are 59632 (Boulder), 59634 (Clancy), 59759 (Whitehall), 59721 (Cardwell), 59638 (Jefferson City) and 59631 (Basin).
Is Elkhorn a real ghost town?
Yes — Elkhorn’s 1880s silver-boom buildings are preserved at Elkhorn Ghost Town State Park, one of Montana’s best-preserved mining ghost towns.
More counties in this state: Towns and villages in Montana.