Harrison County, OH: EPA's radon zone, explained

Harrison County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Nationally, Harrison County ranks higher in radon potential than 78% of rated counties (the 78th percentile).

How Harrison County compares

Harrison County, Ohio is home to about 14,042 people across 402.331 square miles. That works out to roughly 35 people per square mile. By population, Harrison County is the 686th largest of every county sharing its EPA zone — the 36th percentile by population within that zone. Geologically, Harrison County is grouped into EPA Region 5 alongside 523 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. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Harrison County will test well under the action level, and EPA's guidance is to test regardless of zone.

Next steps for a home in Harrison County

For a Harrison 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 Ohio's state radon program

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

Where Harrison 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. If you're unsure why a low zone still deserves a test, the zone explainer covers that directly.