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 29 cities.
Updated August 16, 2026
Highest city
13.1pCi/L
Big Timber
Montana city average
4.7pCi/L
across 29 cities
Above action level
14/ 29
cities
| # | Location | Avg level | Monitors | vs action level |
|---|---|---|---|---|
| 1 | Big Timber | 13.1 pCi/L | 6 | 3.3× over |
| 2 | Scobey | 10.5 pCi/L | 6 | 2.6× over |
| 3 | Thompson Falls | 9.3 pCi/L | 7 | 2.3× over |
| 4 | Big Sky | 7.5 pCi/L | 16 | 1.9× over |
| 5 | Libby | 7.2 pCi/L | 12 | 1.8× over |
| 6 | Red Lodge | 6.7 pCi/L | 17 | 1.7× over |
| 7 | Belgrade | 5.5 pCi/L | 15 | 1.4× over |
| 8 | Columbia Falls | 5.5 pCi/L | 14 | 1.4× over |
| 9 | Anaconda | 4.9 pCi/L | 6 | 1.2× over |
| 10 | Livingston | 4.9 pCi/L | 13 | 1.2× over |
| 11 | Columbus | 4.6 pCi/L | 6 | 1.2× over |
| 12 | Seeley Lake | 4.5 pCi/L | 7 | 1.1× over |
| 13 | Great Falls | 4.2 pCi/L | 15 | 1.0× over |
| 14 | Orchard Homes | 4.0 pCi/L | 22 | 1.0× over |
| ✓ Below EPA action level (4 pCi/L) | ||||
| 15 | Helena | 3.9 pCi/L | 28 | 1.0× under |
| 16 | Butte | 3.8 pCi/L | 17 | 0.9× under |
| 17 | Hamilton | 3.7 pCi/L | 12 | 0.9× under |
| 18 | Stevensville | 3.5 pCi/L | 12 | 0.9× under |
| 19 | Bigfork | 3.2 pCi/L | 19 | 0.8× under |
| 20 | Laurel | 3.1 pCi/L | 16 | 0.8× under |
| 21 | Missoula | 3.1 pCi/L | 39 | 0.8× under |
| 22 | Four Corners | 3.0 pCi/L | 17 | 0.8× under |
| 23 | Bozeman | 2.6 pCi/L | 105 | 0.7× under |
| 24 | Whitefish | 2.6 pCi/L | 16 | 0.6× under |
| 25 | Billings | 2.6 pCi/L | 47 | 0.6× under |
| 26 | Frenchtown | 2.2 pCi/L | 9 | 0.6× under |
| 27 | Lakeside | 2.1 pCi/L | 7 | 0.5× under |
| 28 | Helena West Side | 2.1 pCi/L | 6 | 0.5× under |
| 29 | Kalispell | 1.9 pCi/L | 37 | 0.5× under |