What EPA's radon map says about Harper County

EPA places Harper County in Zone 3 - Low Potential — a predicted county-wide average indoor radon level below 2 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Harper County sits at the 2nd percentile nationally for radon potential — above 2 of every 100 rated counties.

Where Harper County sits nationally

About 3,209 people live in Harper County, Oklahoma, spread over 1,038.584 square miles. That works out to roughly 3 people per square mile. Among counties sharing Harper County's EPA zone, it outranks 5% of them by population. Harper County falls in EPA Radon Region 6, one of 503 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Harper County

Harper County's predicted average sits below the national indoor average of about 1.3 pCi/L, well under EPA's 4 pCi/L action level. A Zone 3 rating means Harper County's county-wide average is predicted low, but EPA is explicit that a meaningful share of homes in low-potential zones still test above the action level — a low zone is not a reason to skip testing.

Testing and mitigation in Harper County

Mitigation cost doesn't depend on Harper County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find Oklahoma's state radon program

Harper County's test kit answers today; a Airthings radon monitor keeps answering for Harper County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Use code RADONZONE-10OFF at checkout for 10% off.

More on how this number was built

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.