Montana Cities Ranked by Indoor Radon Levels
Measured averages from Airthings devices across Montana, USA. Action level: 4 pCi/L — the threshold at which remediation is recommended.
Big Timber has the highest measured indoor radon in Montana at 13.1 pCi/L, based on Airthings measurements across 42 cities.
Updated September 28, 2026
Highest city
13.1pCi/L
Big Timber
Montana city average
5.0pCi/L
across 42 cities
Above action level
22/ 42
cities
| # | Location | Avg level | vs action level |
|---|---|---|---|
| 1 | Big Timber | 13.1 pCi/L | 3.3× over |
| 2 | Scobey | 10.5 pCi/L | 2.6× over |
| 3 | Lewistown | 10.2 pCi/L | 2.6× over |
| 4 | West Yellowstone | 10.0 pCi/L | 2.5× over |
| 5 | Eureka | 9.5 pCi/L | 2.4× over |
| 6 | Thompson Falls | 9.3 pCi/L | 2.3× over |
| 7 | Lolo | 8.8 pCi/L | 2.2× over |
| 8 | Big Sky | 7.5 pCi/L | 1.9× over |
| 9 | Libby | 7.3 pCi/L | 1.8× over |
| 10 | Red Lodge | 6.5 pCi/L | 1.6× over |
| 11 | Sun Prairie | 6.2 pCi/L | 1.6× over |
| 12 | Sidney | 6.0 pCi/L | 1.5× over |
| 13 | Belgrade | 5.5 pCi/L | 1.4× over |
| 14 | Columbia Falls | 5.5 pCi/L | 1.4× over |
| 15 | Polson | 5.4 pCi/L | 1.3× over |
| 16 | Plains | 5.0 pCi/L | 1.3× over |
| 17 | Anaconda | 4.9 pCi/L | 1.2× over |
| 18 | Livingston | 4.9 pCi/L | 1.2× over |
| 19 | Columbus | 4.6 pCi/L | 1.2× over |
| 20 | Seeley Lake | 4.5 pCi/L | 1.1× over |
| 21 | Great Falls | 4.2 pCi/L | 1.1× over |
| 22 | Orchard Homes | 4.0 pCi/L | 1.0× over |
| ✓ Below EPA action level (4 pCi/L) | |||
| 23 | Helena Valley Northwest | 3.9 pCi/L | 1.0× under |
| 24 | Helena | 3.9 pCi/L | 1.0× under |
| 25 | Hamilton | 3.6 pCi/L | 0.9× under |
| 26 | Butte | 3.6 pCi/L | 0.9× under |
| 27 | Stevensville | 3.5 pCi/L | 0.9× under |
| 28 | Bigfork | 3.2 pCi/L | 0.8× under |
| 29 | Laurel | 3.1 pCi/L | 0.8× under |
| 30 | Missoula | 3.1 pCi/L | 0.8× under |
| 31 | Four Corners | 2.9 pCi/L | 0.7× under |
| 32 | Bozeman | 2.6 pCi/L | 0.6× under |
| 33 | Billings | 2.5 pCi/L | 0.6× under |
| 34 | Evergreen | 2.5 pCi/L | 0.6× under |
| 35 | Whitefish | 2.5 pCi/L | 0.6× under |
| 36 | Lakeside | 2.3 pCi/L | 0.6× under |
| 37 | Frenchtown | 2.2 pCi/L | 0.6× under |
| 38 | Three Forks | 2.1 pCi/L | 0.5× under |
| 39 | Helena West Side | 2.1 pCi/L | 0.5× under |
| 40 | Philipsburg | 2.0 pCi/L | 0.5× under |
| 41 | Kalispell | 1.9 pCi/L | 0.5× under |
| 42 | East Missoula | 1.4 pCi/L | 0.3× under |