Population of Counties in Montana (2020)

The most populous county located in the state of Montana is Yellowstone County, home to Billings, which has a population of 160,137 in 2019. Since the time that the last census was taken in 2010, Yellowstone County has seen an increase in the total population of 7.92%. The only other counties in the state of Montana with a population of more than 100,000 are Missoula County (118,791, Gallatin County (111,876), and Flathead County (102,106). All four counties have experienced substantial population growth of at least 7%; Gallatin County grew the most with a 24.79% growth rate.

Montana Counties with the Fewest Residents

The county with the lowest population in the state of Montana is Petroleum County, which has a population of 513 people. Since the last census in 2010, Petroleum County’s population has seen an increase of 4.91%. Following up after Petroleum County, other small counties in Montana include Treasure County (679), Golden Valley County (826), Wibaux County (1,034), and Prairie County (1,087). Of these counties, Petroleum County experienced the most significant growth while Prairie County had the most dramatic decline with a growth rate of -8.11%.

Montana Counties with Rapid Growth

The county with the most significant growth rate in the state of Montana is Gallatin County, which has seen a population growth of 24.79% since the 2010 census was taken, bringing the population up to 111,876 in 2019. Montana has several other counties that have experienced double-digit growth since the census including Madison County (13.91%), Flathead County (12.37%), and Richland County (11.82%). Toole County has seen the lowest population growth, with a loss of 9.17%. )

Name 2020 Population Growth Since 2010
Yellowstone County160,1377.92%
Missoula County118,7918.52%
Gallatin County111,87624.79%
Flathead County102,10612.37%
Cascade County81,6430.17%
Lewis and Clark County68,7008.06%
Ravalli County43,1727.06%
Silver Bow County34,9932.22%
Lake County30,2505.07%
Lincoln County19,7940.50%
Park County16,7367.28%
Hill County16,3471.20%
Glacier County13,7472.44%
Big Horn County13,3383.28%
Jefferson County12,0976.04%
Sanders County11,8443.93%
Custer County11,586-0.92%
Fergus County11,113-4.10%
Roosevelt County11,0595.89%
Richland County10,91311.82%
Carbon County10,7146.47%
Stillwater County9,5344.51%
Beaverhead County9,4041.61%
Deer Lodge County9,131-1.70%
Rosebud County9,063-2.04%
Madison County8,76813.91%
Dawson County8,680-3.02%
Valley County7,4370.80%
Powell County6,968-0.73%
Blaine County6,8074.67%
Teton County6,1621.45%
Broadwater County6,0858.04%
Pondera County5,972-3.07%
Chouteau County5,745-1.12%
Toole County4,853-9.17%
Musselshell County4,6512.11%
Mineral County4,3162.13%
Phillips County4,074-4.19%
Sweet Grass County3,7102.49%
Sheridan County3,4241.66%
Granite County3,3789.68%
Fallon County2,9201.07%
Liberty County2,4303.45%
Wheatland County2,2363.71%
Judith Basin County1,952-5.79%
Meagher County1,866-0.64%
Daniels County1,747-0.11%
Powder River County1,716-1.32%
McCone County1,675-4.01%
Garfield County1,2686.38%
Carter County1,2386.72%
Prairie County1,087-8.11%
Wibaux County1,0342.68%
Golden Valley County826-6.03%
Treasure County679-5.43%
Petroleum County5134.91%