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Radon Levels, Testing and Mitigation in Montana

Montana has 56 counties, with 49 classified as EPA Zone 1 (highest risk). With an average radon level of 8.63 pCi/L, Montana state testing data reveals significantly elevated risks across multiple counties. Testing is highly recommended.

Montana is the 4th most expansive state in terms of size and the 44th most populous. It also happens to be the 48th most densely populated in the entire US.

Montana does have an active radon program, dedicated to educating citizens about the risks associated with the deadly gas. You can find more information on Radon, testing and mitigation at the official page.

8.63
Avg. pCi/L
56
Counties
49
Zone 1 Counties

Montana Radon Map

Montana radon levels by county
Zone 1 — High
Zone 2 — Moderate
Zone 3 — Low

Montana Metro Areas

Explore radon data organized by metro region, including average levels, hotspot cities, and local mitigation professionals.

Billings Metro
5 cities

Most Active Radon Markets in Montana

Cities with the most user-submitted radon test data, ranked by number of submissions.

CityAvg User Radon LevelSubmissions
Butte 10.20 pCi/L 10
Missoula 6.25 pCi/L 8
Florence 11.67 pCi/L 3
Bozeman 10.33 pCi/L 3
Helena 8.67 pCi/L 3
Stevensville 7.67 pCi/L 3
Sidney 7.33 pCi/L 3
Billings 5.33 pCi/L 3
Miles City 3.33 pCi/L 3
Kalispell 7.50 pCi/L 2
Great Falls 4.50 pCi/L 2
Whitefish 4.00 pCi/L 2
Ennis 9.00 pCi/L 1
Livingston No submissions 0

Montana Counties by EPA Radon Zone

All 56 Montana counties with their EPA radon zone classification and user-submitted average radon levels.

Zone 1 — High Risk
Predicted avg. indoor levels > 4.0 pCi/L
Zone 1 49 counties
Beaverhead County Zone 1
Avg: 10.3 pCi/L
Big Horn County Zone 1
Avg:
Blaine County Zone 1
Avg:
Broadwater County Zone 1
Avg: 6.0 pCi/L
Carbon County Zone 1
Avg: 4.0 pCi/L
Carter County Zone 1
Avg:
Cascade County Zone 1
Avg: 4.0 pCi/L
Chouteau County Zone 1
Avg:
Custer County Zone 1
Avg: 3.3 pCi/L
Daniels County Zone 1
Avg:
Dawson County Zone 1
Avg: 9.0 pCi/L
Deer Lodge County Zone 1
Avg: 15.0 pCi/L
Fallon County Zone 1
Avg:
Fergus County Zone 1
Avg:
Flathead County Zone 1
Avg: 7.6 pCi/L
Gallatin County Zone 1
Avg: 9.5 pCi/L
Garfield County Zone 1
Avg:
Glacier County Zone 1
Avg: 4.0 pCi/L
Granite County Zone 1
Avg:
Hill County Zone 1
Avg:
Jefferson County Zone 1
Avg: 7.0 pCi/L
Judith Basin County Zone 1
Avg: 10.0 pCi/L
Lake County Zone 1
Avg: 7.3 pCi/L
Lewis and Clark County Zone 1
Avg: 8.0 pCi/L
Liberty County Zone 1
Avg:
Lincoln County Zone 1
Avg: 16.0 pCi/L
Madison County Zone 1
Avg: 17.0 pCi/L
McCone County Zone 1
Avg:
Meagher County Zone 1
Avg:
Mineral County Zone 1
Avg:
Missoula County Zone 1
Avg: 8.6 pCi/L
Park County Zone 1
Avg:
Phillips County Zone 1
Avg:
Pondera County Zone 1
Avg:
Powder River County Zone 1
Avg:
Powell County Zone 1
Avg: 6.0 pCi/L
Prairie County Zone 1
Avg:
Ravalli County Zone 1
Avg: 9.0 pCi/L
Richland County Zone 1
Avg: 7.3 pCi/L
Roosevelt County Zone 1
Avg: 5.0 pCi/L
Rosebud County Zone 1
Avg:
Sanders County Zone 1
Avg: 11.7 pCi/L
Sheridan County Zone 1
Avg:
Silver Bow County Zone 1
Avg: 10.2 pCi/L
Stillwater County Zone 1
Avg: 6.5 pCi/L
Teton County Zone 1
Avg:
Toole County Zone 1
Avg:
Valley County Zone 1
Avg:
Wibaux County Zone 1
Avg:
Zone 2 — Moderate Risk
Predicted avg. indoor levels 2–4 pCi/L
Zone 2 7 counties
Golden Valley County Zone 2
Avg:
Musselshell County Zone 2
Avg: 10.0 pCi/L
Petroleum County Zone 2
Avg:
Sweet Grass County Zone 2
Avg: 8.5 pCi/L
Treasure County Zone 2
Avg:
Wheatland County Zone 2
Avg:
Yellowstone County Zone 2
Avg: 5.5 pCi/L

Montana Cities & Towns

Browse radon data for individual cities across Montana. Each city page includes user-submitted radon levels, local contractors, and mitigation resources.

Absarokee Acton Alberton Alzada Anaconda Angela Antelope Arlee Ashland Bainville Baker Ballantine Bearcreek Belfry Belgrade Belt Biddle Big Arm Big Sandy Big Timber Bigfork Bighorn Billings Birney Black Eagle Bloomfield Bonner Boulder Box Elder Boyes Bozeman Brady Bridger Broadus Broadview Brockton Brockway Browning Brusett Buffalo Busby Butte Bynum Cameron Canyon Creek Capitol Cardwell Carter Cascade Charlo Chester Chinook Choteau Circle Clancy Clinton Coffee Creek Cohagen Columbia Falls Columbus Condon Conner Conrad Corvallis Crow Agency Culbertson Custer Cut Bank Dagmar Darby Dayton Decker Deer Lodge Denton Dillon Divide Dixon Dodson Drummond Dutton East Helena Edgar Ekalaka Elmo Emigrant Ennis Essex Eureka Fairfield Fairview Fallon Fishtail Flaxville Florence Floweree Forest Grove Forsyth Fort Benton Fort Peck Fort Shaw Frazer Frenchtown Froid Fromberg Galata Gallatin Gateway Gardiner Garrison Garryowen Geraldine Geyser Gildford Glasgow Glendive Glentana Gold Creek Grass Range Great Falls Greycliff Hall Hamilton Hammond Hardin Harlem Hathaway Havre Helena Helmville Heron Highwood Hilger Hingham Hinsdale Hobson Hogeland Homestead Hot Springs Huntley Huson Hysham Ingomar Inverness Ismay Jackson Joliet Joplin Jordan Judith Gap Kalispell Kevin Kila Kinsey Kremlin Lakeside Lambert Larslan Laurel Lavina Ledger Lewistown Libby Lima Lincoln Lindsay Livingston Lloyd Lodge Grass Lolo Loma Lonepine Loring Lothair Malmstrom A F B Malta Manhattan Marion Martin City Martinsdale Mc Leod Medicine Lake Melville Mildred Miles City Missoula Moccasin Molt Monarch Moore Mosby Musselshell Nashua Neihart Norris Noxon Nye Oilmont Olive Opheim Otter Outlook Ovando Park City Peerless Pendroy Philipsburg Plains Plentywood Plevna Polaris Polebridge Polson Pompeys Pillar Poplar Powderville Power Pray Proctor Radersburg Rapelje Ravalli Raynesford Red Lodge Redstone Reed Point Reserve Rexford Richey Richland Roberts Rollins Ronan Roscoe Rosebud Roundup Roy Rudyard Ryegate Saco Saint Ignatius Saint Regis Saint Xavier Saltese Sand Coulee Sand Springs Sanders Savage Scobey Seeley Lake Shawmut Shelby Shepherd Sheridan Sidney Silver Gate Silver Star Somers Stanford Stevensville Stockett Sula Sun River Sunburst Superior Sweet Grass Teigen Terry Thompson Falls Three Forks Toston Townsend Trout Creek Troy Turner Twin Bridges Two Dot Valier Vandalia Vaughn Victor Vida Virginia City Volborg West Yellowstone Westby White Sulphur Springs Whitefish Whitehall Whitetail Whitewater Whitlash Wibaux Wilsall Winifred Winnett Wisdom Wise River Wolf Creek Wolf Point Worden Wyola Zortman Zurich

Frequently Asked Questions About Radon in Montana

What radon level is considered "high"?
The EPA action level is 4.0 pCi/L — many homeowners also choose to fix levels between 2.0 and 4.0 pCi/L. Any home with levels at or above 4.0 pCi/L should be mitigated.
How much does radon mitigation cost in Montana?
Radon mitigation typically costs between $800 and $2,500, depending on foundation type and radon severity. A standard sub-slab depressurization system usually falls in the $1,000–$1,500 range.
Does mitigation actually work?
Yes — properly installed systems typically reduce radon levels by up to 99%. A post-mitigation test confirms the system is working correctly, and many homeowners re-test periodically.
Should I test again after mitigation?
Yes. A post-mitigation test is the proof your system is working. The EPA recommends testing within 30 days of installation and retesting every two years.
What EPA Radon Zone is my Montana county in?
Montana counties are classified into three EPA Radon Zones. Zone 1 (highest risk, >4 pCi/L) indicates the most concern. Zone 2 (moderate, 2–4 pCi/L) and Zone 3 (lowest, <2 pCi/L) round out the classification. Use the county directory above to find your specific county's zone and data.

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