Radon zones in Montana
Last updated
EPA’s Map of Radon Zones places 56 Montana counties in its three radon potential zones: 49 in Zone 1 (highest), 7 in Zone 2 (moderate), and 0 in Zone 3 (low).
What this means for Montana homes
Most Montana counties fall in Zone 1. EPA predicts average indoor screening levels above 4 pCi/L across much of Montana, so elevated radon is common. Testing is especially worthwhile here, and radon-resistant construction features make sense for new homes.
EPA’s guidance is the same everywhere: test your home, fix it if the level is 4 pCi/L or higher, and consider fixing between 2 and 4 pCi/L. The zone map is from 1993 and should not be used to decide whether a single home needs testing.
Montana radon program
EPA lists the following state contact for Montana: MT Department of Environmental Quality, Energy: Radon, phone 406-444-6592. Website: deq.mt.gov/Energy/radon. State programs can tell you about local testing data, free or discounted test kits, disclosure rules for home sales, and credentialed radon professionals.
Montana counties and their EPA radon zones
| County | EPA radon zone |
|---|---|
| Beaverhead County | Zone 1 |
| Big Horn County | Zone 1 |
| Blaine County | Zone 1 |
| Broadwater County | Zone 1 |
| Carbon County | Zone 1 |
| Carter County | Zone 1 |
| Cascade County | Zone 1 |
| Chouteau County | Zone 1 |
| Custer County | Zone 1 |
| Daniels County | Zone 1 |
| Dawson County | Zone 1 |
| Deer Lodge County | Zone 1 |
| Fallon County | Zone 1 |
| Fergus County | Zone 1 |
| Flathead County | Zone 1 |
| Gallatin County | Zone 1 |
| Garfield County | Zone 1 |
| Glacier County | Zone 1 |
| Golden Valley County | Zone 2 |
| Granite County | Zone 1 |
| Hill County | Zone 1 |
| Jefferson County | Zone 1 |
| Judith Basin County | Zone 1 |
| Lake County | Zone 1 |
| Lewis and Clark County | Zone 1 |
| Liberty County | Zone 1 |
| Lincoln County | Zone 1 |
| Madison County | Zone 1 |
| McCone County | Zone 1 |
| Meagher County | Zone 1 |
| Mineral County | Zone 1 |
| Missoula County | Zone 1 |
| Musselshell County | Zone 2 |
| Park County | Zone 1 |
| Petroleum County | Zone 2 |
| Phillips County | Zone 1 |
| Pondera County | Zone 1 |
| Powder River County | Zone 1 |
| Powell County | Zone 1 |
| Prairie County | Zone 1 |
| Ravalli County | Zone 1 |
| Richland County | Zone 1 |
| Roosevelt County | Zone 1 |
| Rosebud County | Zone 1 |
| Sanders County | Zone 1 |
| Sheridan County | Zone 1 |
| Silver Bow County | Zone 1 |
| Stillwater County | Zone 1 |
| Sweet Grass County | Zone 2 |
| Teton County | Zone 1 |
| Toole County | Zone 1 |
| Treasure County | Zone 2 |
| Valley County | Zone 1 |
| Wheatland County | Zone 2 |
| Wibaux County | Zone 1 |
| Yellowstone County | Zone 2 |
County names follow the 2020 Census. Zones from the EPA Map of Radon Zones (text version). Rows marked “zone of” use the zone EPA gave the predecessor or surrounding county.
Next steps: read how to test your home, check a result with the level calculator, or look up a single address by ZIP code.