Jefferson County area

Population and density of Jefferson County

The Census Bureau estimates that 13,329 people lived in Jefferson County on July 1, 2025. That ranks #2,271 of 3,222 county equivalents nationally and #15 of 56 in Montana. Since the April 1, 2020 estimates base of 12,081, the population has grown by 1,248 (+10.3%), compared with +5.6% for Montana as a whole.

With 1,657 square miles of land, that is 8 people per square mile (3.1 per km²), placing Jefferson County #2,717 nationally for density and #11 in Montana. The median county equivalent has 47 people per square mile; the Montana median is 2.8. Put another way, there are about 80 acres of land per resident.

U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.

Cities and towns in Jefferson County

2 incorporated places lie at least partly in Jefferson County. Together they are home to 2,436 people (18.3%); the other 10,893 (81.7%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Boulder city, with 1,305 residents in the county. Among places with at least 1,000 residents in 2020, Whitehall town grew fastest since then (+12.8%).

Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Jefferson County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.

Metropolitan area

Jefferson County is an outlying county of the Helena, MT Metropolitan Statistical Area. Its 3 county equivalents have 97,153 residents on 6,307.7 square miles of land; Jefferson County accounts for 26.3% of the land and 13.7% of the residents. By combined land it ranks #30 of 393 metropolitan areas, and #374 by population.

ZIP codes

9 ZIP Code Tabulation Areas have land in Jefferson County; 6 of them have most of their land inside the county, and the others mainly cover neighboring areas.

596315963259634596355963859701597215975259759

ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.

Counties bordering Jefferson County

Jefferson County shares a land border with 7 county equivalents. It has more land than 3 of them. The largest neighbor is Madison County (3,588.2 mi²) and the smallest is Silver Bow County (718 mi²). Together with its neighbors, Jefferson County forms a block of 16,282 mi² of land, of which it holds 10.2%.

How big is Jefferson County compared with U.S. states?

Jefferson County has more land than 1 of the 50 states. It is about 1.6 times the land area of Rhode Island (1,033.9 mi²), while Delaware, the next larger state, has 1.2 times as much land (1,948.6 mi²). Montana’s county land could hold about 88 areas the size of Jefferson County.

Another way to picture it: the same land area would fill a square about 40.7 miles (65.5 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.

State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.

What stands out about Jefferson County?

Jefferson County has more land than 2,857 of the other 3,221 county equivalents in the dataset.

A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.

Does including water change its rank?

Using land plus water places Jefferson County at #406 nationally by total area, 41 places farther from the top than its land rank. Other county equivalents gain more area when their water measurements are included.

Its water share is 0.1%, compared with a national county-equivalent median of 1.2% — 1 percentage points lower. This describes the statistical geography’s land/water mix, not flood exposure or developable land.

Closest positions in the national land ranking

These entries sit immediately beside Jefferson County in the national ranking. They can be in different states and are not necessarily geographic neighbors.

Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.