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

EPA's own radon map rates Knox County zone 1 - highest potential, predicting a county-wide average indoor level above 4 pCi/L. Nationally that's the 92nd percentile for radon potential — Knox County outranks 92% of every county EPA has rated.

How Knox County compares

Knox County, Ohio is home to about 63,848 people across 525.499 square miles. Population density there runs about 121 people per square mile. By population, Knox County is the 262nd largest of every county sharing its EPA zone — the 75th percentile by population within that zone. Knox County falls in EPA Radon Region 5, one of 524 counties nationally EPA assigns to that same geologic province.

Why the zone isn't the answer by itself

Knox County's predicted average sits above EPA's own action level of 4 pCi/L — the concentration at which EPA recommends fixing a home — versus a national average around 1.3 pCi/L indoors and 0.4 pCi/L outdoors. Being in Zone 1 raises the odds Knox County homes test above the action level, but it does not mean any specific house does — EPA recommends every home be tested, in every zone, because the only way to know is to test.

If Knox County tests above the action level

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

Where Knox 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 Knox County carries, the zone explainer covers what it does and doesn't tell you about any one house.