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

Rosebud County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Rosebud County sits at the 74th percentile nationally for radon potential — above 74 of every 100 rated counties.

Rosebud County by the numbers

Rosebud County, Montana is home to about 8,194 people across 5,008.135 square miles. That works out to roughly 2 people per square mile. By population, Rosebud County is the 817th largest of every county sharing its EPA zone — the 23rd percentile by population within that zone. Rosebud County falls in EPA Radon Region 8, one of 291 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Rosebud 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. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Rosebud County will test well under the action level, and EPA's guidance is to test regardless of zone.

If Rosebud County tests above the action level

For a Rosebud 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 Rosebud County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Rosebud 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 Rosebud County's figures come from

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. Whatever zone Rosebud County carries, the zone explainer covers what it does and doesn't tell you about any one house.