Silver Bow County, MT: EPA's radon zone, explained

EPA's own radon map rates Silver Bow County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally, Silver Bow County ranks higher in radon potential than 87% of rated counties (the 87th percentile).

Where Silver Bow County sits nationally

Silver Bow County, Montana is home to about 36,134 people across 717.99 square miles. Averaged across its land area, Silver Bow County runs about 50 people per square mile. By population, Silver Bow County is the 415th largest of every county sharing its EPA zone — the 61st percentile by population within that zone. Geologically, Silver Bow County is grouped into EPA Region 8 alongside 290 other counties that share its rock and soil setting.

What this actually means for a house in Silver Bow County

Silver Bow 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 Silver Bow 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 Silver Bow County tests above the action level

For a Silver Bow 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 Silver Bow County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Silver Bow 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 Silver Bow 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. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.