What EPA's radon map says about Harrison County

EPA places Harrison 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. That puts Harrison County in the 79th percentile nationally for radon potential — higher than 79% of the counties EPA has rated.

Where Harrison County sits nationally

About 14,626 people live in Harrison County, Iowa, spread over 696.874 square miles. Population density there runs about 21 people per square mile. Among counties sharing Harrison County's EPA zone, it outranks 37% of them by population. Geologically, Harrison County is grouped into EPA Region 7 alongside 411 other counties that share its rock and soil setting.

Zone vs. an actual test

Where the national indoor average runs about 1.3 pCi/L, Harrison County's Zone 1 rating puts its predicted county average above EPA's 4 pCi/L action level itself. That doesn't mean every Harrison 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.

Next steps for a home in Harrison County

Mitigation cost doesn't depend on Harrison 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 Iowa's state radon program

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

More on how this number was built

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