Ohio radon map by county: EPA zones and test results

Ohio has two radon maps, and they answer different questions. EPA's Map of Radon Zones, drawn in 1993, predicts a county-wide average from geology, aerial radioactivity, soils, foundation types, and the indoor measurements available at the time. The Ohio Department of Health's radon dashboard reports what Ohio-licensed radon professionals have actually measured since 2010, roughly 508,000 pre-mitigation tests statewide. The table below puts both side by side for all 88 counties, followed by the three Northern Kentucky counties across the river from Cincinnati.

Reading the zones. Zone 1 counties have a predicted average indoor screening level above 4 pCi/L, EPA's action level. Zone 2 counties are predicted between 2 and 4 pCi/L. Ohio has no Zone 3 county: 53 counties are Zone 1 and 35 are Zone 2. Across every test reported to ODH, about 35 percent read above 4.0 pCi/L.

Where the two maps disagree. Six counties report more than half of their tests above 4.0: Fairfield, Pickaway, Madison, Coshocton, Licking, and Morrow, all Zone 1. But the zone is not destiny. Hamilton County is Zone 1 and reports about 22 percent above 4.0, while its Zone 2 neighbor Clermont reports about 36 percent. Adams County is Zone 1 with about 12 percent, and Cuyahoga, a Zone 2 county with more than 49,000 tests, reports about 15 percent. That is why EPA says its map should not decide whether an individual home is tested, and why ODH recommends testing every occupied building that touches the ground.

How to read the numbers. The share above 4.0 is the most useful single figure. The average is an arithmetic mean, which a handful of very high homes can pull upward, and counties with fewer than 200 reported tests are marked as small samples. Figures were pulled from the ODH dashboard in September 2026; ODH updates it monthly. For ZIP-level results around Cincinnati, see our radon levels by ZIP code table.

Northern Kentucky

Boone, Kenton, and Campbell counties are all Zone 2 on EPA's Kentucky map, while Pendleton County to their south is Zone 1. Kentucky publishes no county results dashboard comparable to Ohio's, so the rows above carry the zone only. County radon handouts from the University of Kentucky's BREATHE program note that radon is a problem in many areas of each county. Anyone who tests or mitigates for pay in Kentucky must be certified through NRPP or NRSB and registered with the state under KRS 211.9101 to 211.9135.

What to do with your county's numbers

A county figure sets expectations; it cannot tell you your own level. Houses on the same street regularly test far apart, so the next step is the same everywhere on this map:

• Test. Ohio homeowners can order a free kit through the Ohio Department of Health at ohio.radon.com. Place it in the lowest level you use as living space, with windows and outside doors closed for 12 hours first. Our heating-season testing guide covers placement.
• Use licensed help for a sale. In Ohio, testing for someone else requires an ODH radon license; ODH's Hire a Professional page links a map of licensed testers and mitigation contractors. See our radon testing page for professional options in Greater Cincinnati.
• Act on a high result. At 4.0 pCi/L or higher, EPA recommends a follow-up test and then a fix. The radon mitigation systems page explains how that works, and our answer on whether radon is dangerous covers the health side.

If you are in Greater Cincinnati or Northern Kentucky and your result is back, call or text us with the number and we will walk through what comes next.