Is Harrison County, MO a radon risk area?

EPA's own radon map rates Harrison County zone 2 - moderate potential, predicting a county-wide average indoor level between 2 and 4 pCi/L. Nationally that's the 38th percentile for radon potential — Harrison County outranks 38% of every county EPA has rated.

How Harrison County compares

About 8,186 people live in Harrison County, Missouri, spread over 722.517 square miles. That works out to roughly 11 people per square mile. Rank 864 by population within its EPA zone puts Harrison County at the 16th percentile among zone peers. EPA's geology-based Region 7 groups Harrison County with 411 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Harrison County

EPA's Zone 2 rating for Harrison County sits below its own 4 pCi/L action level but above the national indoor average of about 1.3 pCi/L. Middle-of-the-pack doesn't mean risk-free for any one Harrison County address — a moderate county average still leaves individual homes to test either side of it.

Next steps for a home in Harrison County

Nothing about Harrison County's EPA zone changes the mitigation number: $800–$2,500 nationally (around $1,200 typical), set by the house's foundation rather than the county it sits in — and only relevant once a test actually clears 4 pCi/L.

Find Missouri'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. Use code RADONZONE-10OFF at checkout for 10% off.

More on how this number was built

The methodology guide shows exactly which EPA and Census sources feed Harrison County's numbers. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.