Riley County, KS: EPA's radon zone, explained

EPA places Riley County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Riley County sits at the 92nd percentile nationally for radon potential — above 92 of every 100 rated counties.

Where Riley County sits nationally

Riley County, Kansas is home to about 72,557 people across 609.66 square miles. Population density there runs about 119 people per square mile. By population, Riley County is the 242nd largest of every county sharing its EPA zone — the 77th percentile by population within that zone. EPA's geology-based Region 7 groups Riley County with 411 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Riley County

Riley 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 Riley 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 Riley County tests above the action level

For a Riley 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 Kansas's state radon program

For Riley County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Riley 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 Riley 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 Riley County carries, the zone explainer covers what it does and doesn't tell you about any one house.