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

Guernsey County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Nationally that's the 87th percentile for radon potential — Guernsey County outranks 87% of every county EPA has rated.

Where Guernsey County sits nationally

Guernsey County, Ohio is home to about 38,219 people across 522.242 square miles. Averaged across its land area, Guernsey County runs about 73 people per square mile. By population, Guernsey County is the 393rd largest of every county sharing its EPA zone — the 63rd percentile by population within that zone. EPA's geology-based Region 5 groups Guernsey County with 523 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Guernsey County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. 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 Guernsey County will test well under the action level, and EPA's guidance is to test regardless of zone.

Testing and mitigation in Guernsey County

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