Facts & Figures • Geography
Updated: February 12, 2026
Montana Cities and Counties
An introduction for sixth-grade students.
History of Montana Counties
Montana became a United States territory in 1864 and became a state in 1889, during a time of mining, ranching, and railroad expansion in the West.
Some of the first counties created in Montana included Beaverhead, Chouteau, Deer Lodge, Jefferson, Lewis and Clark, Madison, and Missoula, which helped organize local government as more people settled in different areas.
Over time, new counties were formed as homesteaders, miners, and towns spread out, so that people did not have to travel as far to reach a courthouse or county seat.
The last county to be created was Petroleum County in 1925, when part of Fergus County was separated after oil discoveries at the Cat Creek Oil Field made the area more important.
County Size: Largest and Smallest by Area
Today Montana has 56 counties, and they cover a wide range of sizes from very large to quite small.
The largest county in Montana by land area is Beaverhead County in the southwest part of the state, which covers about 5,542 square miles of mountains, valleys, and ranch land.
One of the smallest counties in land area is Silver Bow County, home to the city of Butte, which covers about 718 square miles and has a combined city‑county government.
Deer Lodge County is another relatively small county that is also a consolidated city‑county, with its main community in and around the town of Anaconda.
County Population and Density
According to the 2020 Census, Montana's total population was 1,084,225 people, spread across all 56 counties.
Yellowstone County, which includes the city of Billings, is the most populated county in Montana, with 164,731 people counted in 2020 and more than 170,000 people in recent estimates.
In 2010, Yellowstone County had 147,972 residents and a population density of about 56 people per square mile, showing how it has grown over the last decade.
By comparison, Petroleum County is the least populated county in Montana, with only 496 people counted in 2020—less than one person per square mile—making it one of the least densely populated counties in the entire United States.
Examples of Different Counties
The table below shows how some Montana counties differ in population and size.
| County | Approximate 2026 Population | Area (square miles) | People per square mile | Notes |
|---|---|---|---|---|
| Yellowstone | About 173,000 people | About 2,600 | About 60–66 | Most populated county; includes Billings. |
| Gallatin | About 129,000 people | About 2,600 | About 50 | Fast‑growing county around Bozeman. |
| Beaverhead | About 10,240 people | 5,542 | About 2 people per square mile | Largest county by area. |
| Silver Bow | About 36,000 people | 718 | About 50 people per square mile | Small in area; includes the city of Butte. |
| Petroleum | About 500 people | About 1,700 | Less than 1 person per square mile | Least populated county in Montana. |
Where to Learn More
The U.S. Census Bureau provides QuickFacts and state profiles where students and teachers can explore up‑to‑date information about Montana, its counties, and its cities, including population counts and other data.
Montana state geographic and mapping services share tables and maps that show the area of each county and changes over time, which can help people understand how land and population are distributed across the state.
Educational websites designed for kids explain topics like how Petroleum County was formed and why some counties have grown faster than others, using simple language and examples.
Updated: February 12, 2026