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

EPA places Hardin 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. Rank it against the rest of the country and Hardin County lands in the 85th percentile for radon potential.

Hardin County by the numbers

Hardin County, Ohio is home to about 30,402 people across 470.285 square miles. Population density there runs about 65 people per square mile. By population, Hardin County is the 464th largest of every county sharing its EPA zone — the 56th percentile by population within that zone. Hardin County falls in EPA Radon Region 5, one of 524 counties nationally EPA assigns to that same geologic province.

What this actually means for a house in Hardin County

Hardin County carries a Zone 1 label because its predicted average clears 4 pCi/L outright — three-plus times the 0.4 pCi/L typical outdoors and above the 1.3 pCi/L most homes see. 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 Hardin County will test well under the action level, and EPA's guidance is to test regardless of zone.

Testing and mitigation in Hardin County

For a Hardin 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 Hardin County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Hardin 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 Hardin County's figures come from

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