Gallatin County, MT radon potential

EPA's own radon map rates Gallatin County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Rank it against the rest of the country and Gallatin County lands in the 95th percentile for radon potential.

Gallatin County by the numbers

Gallatin County, Montana is home to about 126,984 people across 2,605.354 square miles. Population density there runs about 49 people per square mile. Within its own EPA zone, Gallatin County is bigger by population than 85% of the counties that share it. EPA's geology-based Region 8 groups Gallatin County with 290 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Gallatin County

Gallatin County carries a Zone 1 label because its predicted average clears 4 pCi/L outright — three-plus times the 0.4 pCi/L typical outdoors and above the 1.3 pCi/L most homes see. That doesn't mean every Gallatin County house tests high — a zone is a county-wide prediction, never a single-home reading — but it's a reason to test sooner rather than let it wait.

Testing and mitigation in Gallatin County

A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.

Find Montana's state radon program

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

The methodology guide shows exactly which EPA and Census sources feed Gallatin County's numbers. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.