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 43 cities.

Updated October 19, 2026

Highest city

13.1pCi/L

Big Timber

Montana city average

4.9pCi/L

across 43 cities

Above action level

21/ 43

cities

Montana Cities Ranked by Indoor Radon Levels
#	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	8.4 pCi/L	2.1× 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	5.4 pCi/L	1.4× over
15	Plains	5.0 pCi/L	1.3× over
16	Anaconda	4.9 pCi/L	1.2× over
17	Livingston	4.9 pCi/L	1.2× over
18	Polson	4.8 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
✓ Below EPA action level (4 pCi/L)
22	Orchard Homes	4.0 pCi/L	1.0× under
23	Helena Valley Northwest	3.9 pCi/L	1.0× under
24	Helena	3.9 pCi/L	1.0× under
25	Hamilton	3.5 pCi/L	0.9× under
26	Stevensville	3.5 pCi/L	0.9× under
27	Butte	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	3.0 pCi/L	0.8× under
31	Four Corners	3.0 pCi/L	0.7× under
32	Ronan	2.8 pCi/L	0.7× under
33	Bozeman	2.6 pCi/L	0.7× under
34	Evergreen	2.5 pCi/L	0.6× under
35	Whitefish	2.5 pCi/L	0.6× under
36	Billings	2.5 pCi/L	0.6× under
37	Lakeside	2.3 pCi/L	0.6× under
38	Helena West Side	2.1 pCi/L	0.5× under
39	Three Forks	2.1 pCi/L	0.5× under
40	Frenchtown	2.0 pCi/L	0.5× under
41	Philipsburg	2.0 pCi/L	0.5× under
42	Kalispell	1.9 pCi/L	0.5× under
43	East Missoula	1.4 pCi/L	0.3× under