Gilpin County, CO: EPA's radon zone, explained

EPA's own radon map rates Gilpin County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally that's the 72nd percentile for radon potential — Gilpin County outranks 72% of every county EPA has rated.

Where Gilpin County sits nationally

Gilpin County, Colorado is home to about 5,963 people across 150.023 square miles. Averaged across its land area, Gilpin County runs about 40 people per square mile. By population, Gilpin County is the 883rd largest of every county sharing its EPA zone — the 17th percentile by population within that zone. Geologically, Gilpin County is grouped into EPA Region 8 alongside 290 other counties that share its rock and soil setting.

Why the zone isn't the answer by itself

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Gilpin County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. That doesn't mean every Gilpin 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.

If Gilpin County tests above the action level

For a Gilpin 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 Colorado's state radon program

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

Where Gilpin 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 Gilpin County carries, the zone explainer covers what it does and doesn't tell you about any one house.