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

EPA's own radon map rates Phillips County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Phillips County sits at the 70th percentile nationally for radon potential — above 70 of every 100 rated counties.

Phillips County by the numbers

Phillips County, Colorado is home to about 4,488 people across 687.928 square miles. Population density there runs about 7 people per square mile. By population, Phillips County is the 936th largest of every county sharing its EPA zone — the 12th percentile by population within that zone. EPA's geology-based Region 8 groups Phillips County with 290 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Phillips County

Phillips 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 Phillips 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 Phillips County tests above the action level

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

Where Phillips County's figures come from

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