Ohio has some of the highest indoor radon in the country — but the risk isn’t uniform. Using radon test results reported to the CDC between 2008 and 2017, here’s how Ohio counties actually compare, which ones run highest, and why every home needs testing regardless of its county’s average.
The highest-radon counties in Ohio
Among the Ohio counties we serve, these have the highest average indoor radon levels (CDC, 2008–2017):
- Licking County — 15.5 pCi/L (11.9× the U.S. average), covering Newark. Licking County radon →
- Richland County — 11.0 pCi/L (8.5× the U.S. average), covering Mansfield. Richland County radon →
- Fairfield County — 10.9 pCi/L (8.4× the U.S. average), covering Lancaster. Fairfield County radon →
- Franklin County — 9.5 pCi/L (7.3× the U.S. average), covering Columbus and Dublin. Franklin County radon →
- Stark County — 8.0 pCi/L (6.2× the U.S. average), covering Canton. Stark County radon →
For context, the EPA recommends fixing any home at or above 4.0 pCi/L. Licking County alone averages 15.5 pCi/L — 11.9× the U.S. average of 1.3 — and 11 of the 13 counties we serve average above the action level, meaning the typical home in them needs a mitigation system.
Lower-average counties still aren’t “safe”
Some Ohio counties we serve test lower on average:
- Mahoning County — 3.2 pCi/L, covering Youngstown. Mahoning County radon →
- Cuyahoga County — 3.0 pCi/L, covering Cleveland and Euclid. Cuyahoga County radon →
But a below-average county is not a safe county. Radon depends on your specific home’s foundation, soil, and construction — elevated readings turn up in every county. A short-term test kit ($15–30) is the only way to know your home’s level.
How we know these numbers
These county averages come from the CDC National Environmental Public Health Tracking Network, which aggregates radon test results reported by laboratories. The figures reflect mean pre-mitigation indoor radon levels measured between 2008 and 2017 — real tested homes, not models or predictions. You can see the full county-by-county breakdown on our Ohio radon levels by county page.
What to do next
Wherever you live in Ohio: (1) test your home with a short-term kit or a professional measurement; (2) if your result is at or above 4.0 pCi/L, mitigate — an active sub-slab depressurization system typically cuts indoor radon by 70–99%; (3) re-test after install to confirm. Ohio Radon Experts routes you to an NRPP-certified partner contractor for any of these steps. Find your county’s radon level →