Fallon County, MT: EPA's radon zone, explained

EPA places Fallon County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally, Fallon County ranks higher in radon potential than 69% of rated counties (the 69th percentile).

Fallon County by the numbers

Fallon County, Montana is home to about 2,946 people across 1,620.595 square miles. Population density there runs about 2 people per square mile. By population, Fallon County is the 982nd largest of every county sharing its EPA zone — the 8th percentile by population within that zone. Fallon County falls in EPA Radon Region 8, one of 291 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

Fallon County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. Being in Zone 1 raises the odds Fallon County homes test above the action level, but it does not mean any specific house does — EPA recommends every home be tested, in every zone, because the only way to know is to test.

If Fallon County tests above the action level

For a Fallon County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find Montana's state radon program

For Fallon County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Fallon County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Use code RADONZONE-10OFF at checkout for 10% off.

Where Fallon County's figures come from

Fallon County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Fallon County carries, the zone explainer covers what it does and doesn't tell you about any one house.