Radon in Ohio: radon map by county
EPA's Map of Radon Zones puts 53 of Ohio's 88 counties in Zone 1 (predicted average indoor radon above 4 pCi/L), 35 in Zone 2 and 0 in Zone 3. Of 84,325 building tests that radon laboratories reported for 2008 to 2017, 51.6% were at or above EPA's 4 pCi/L action level, against 36.5% nationally (number 5 of 42 states with 1,000+ tests). The highest county share is Pickaway County (81.4% of 154 tests).
Radon by county in Ohio
| County | EPA zone | Lab tests | Median | 4+ pCi/L |
|---|---|---|---|---|
| Adams County | Zone 1 | 19 | 3.8 | 50% |
| Allen County | Zone 1 | 185 | 5.0 | 56.7% |
| Ashland County | Zone 1 | 276 | 5.4 | 62.9% |
| Ashtabula County | Zone 2 | 282 | 2.5 | 34.4% |
| Athens County | Zone 2 | 181 | 3.1 | 38.1% |
| Auglaize County | Zone 1 | 113 | 6.5 | 71.2% |
| Belmont County | Zone 1 | 723 | 3.6 | 45.2% |
| Brown County | Zone 2 | 51 | 3.3 | 47.1% |
| Butler County | Zone 1 | 1,552 | 4.4 | 54.3% |
| Carroll County | Zone 1 | 368 | 4.8 | 57.4% |
| Champaign County | Zone 1 | 412 | 6.8 | 71.1% |
| Clark County | Zone 1 | 1,123 | 4.9 | 57.5% |
| Clermont County | Zone 2 | 1,168 | 4.0 | 50% |
| Clinton County | Zone 1 | 80 | 4.2 | 52.4% |
| Columbiana County | Zone 1 | 537 | 3.8 | 49.1% |
| Coshocton County | Zone 1 | 95 | 5.1 | 58.9% |
| Crawford County | Zone 1 | 175 | 4.7 | 59.5% |
| Cuyahoga County | Zone 2 | 8,861 | 2.0 | 21.7% |
| Darke County | Zone 1 | 189 | 5.6 | 63.7% |
| Defiance County | Zone 2 | 55 | 3.8 | 48.6% |
| Delaware County | Zone 1 | 3,158 | 6.4 | 72.2% |
| Erie County | Zone 2 | 1,436 | 4.4 | 54.5% |
| Fairfield County | Zone 1 | 1,004 | 7.4 | 76.8% |
| Fayette County | Zone 1 | 12 | 5.5 | 58.3% |
| Franklin County | Zone 1 | 13,807 | 6.8 | 71.9% |
| Fulton County | Zone 2 | 56 | 3.1 | 45.2% |
| Gallia County | Zone 2 | 16 | 3.0 | 33.3% |
| Geauga County | Zone 2 | 1,382 | 2.4 | 23.4% |
| Greene County | Zone 1 | 1,785 | 4.9 | 58.6% |
| Guernsey County | Zone 1 | 93 | 3.6 | 44.4% |
| Hamilton County | Zone 1 | 3,085 | 2.8 | 34.7% |
| Hancock County | Zone 1 | 1,221 | 3.7 | 46.2% |
| Hardin County | Zone 1 | 42 | 3.4 | 43.3% |
| Harrison County | Zone 1 | 37 | 4.1 | 50% |
| Henry County | Zone 2 | 35 | 5.3 | 61.8% |
| Highland County | Zone 2 | 53 | 4.8 | 56.7% |
| Hocking County | Zone 2 | 41 | 4.0 | 53.3% |
| Holmes County | Zone 1 | 58 | 5.8 | 64.2% |
| Huron County | Zone 1 | 692 | 4.9 | 59.4% |
| Jackson County | Zone 2 | 35 | 3.3 | 41.7% |
| Jefferson County | Zone 1 | 240 | 3.9 | 49.8% |
| Knox County | Zone 1 | 987 | 8.1 | 72% |
| Lake County | Zone 2 | 2,194 | 2.4 | 27.2% |
| Lawrence County | Zone 2 | 53 | 2.5 | 30.3% |
| Licking County | Zone 1 | 3,431 | 7.0 | 71.2% |
| Logan County | Zone 1 | 487 | 7.9 | 73.6% |
| Lorain County | Zone 2 | 2,937 | 3.6 | 45.4% |
| Lucas County | Zone 2 | 1,752 | 3.0 | 40.2% |
| Madison County | Zone 1 | 423 | 5.7 | 67.4% |
| Mahoning County | Zone 2 | 556 | 2.5 | 23.4% |
| Marion County | Zone 1 | 192 | 6.4 | 65.3% |
| Medina County | Zone 2 | 1,942 | 3.5 | 43.4% |
| Meigs County | Zone 2 | 16 | 2.7 | 20% |
| Mercer County | Zone 1 | 98 | 5.1 | 57.7% |
| Miami County | Zone 1 | 513 | 6.1 | 65.2% |
| Monroe County | Zone 2 | 40 | 5.0 | 58.3% |
| Montgomery County | Zone 1 | 2,223 | 4.0 | 50.3% |
| Morgan County | Zone 2 | 9 | 3.3 | 30% |
| Morrow County | Zone 1 | 143 | 5.7 | 65% |
| Muskingum County | Zone 1 | 339 | 4.9 | 56.3% |
| Noble County | Zone 2 | 34 | 2.2 | 31% |
| Ottawa County | Zone 2 | 479 | 2.9 | 40.3% |
| Paulding County | Zone 2 | 12 | 3.2 | 23.1% |
| Perry County | Zone 1 | 78 | 3.8 | 48.9% |
| Pickaway County | Zone 1 | 154 | 9.5 | 81.4% |
| Pike County | Zone 1 | 33 | 4.5 | 56.1% |
| Portage County | Zone 2 | 1,561 | 3.2 | 39.3% |
| Preble County | Zone 1 | 133 | 5.5 | 62.7% |
| Putnam County | Zone 2 | 74 | 4.8 | 59.6% |
| Richland County | Zone 1 | 998 | 5.2 | 62.2% |
| Ross County | Zone 1 | 251 | 7.0 | 67.1% |
| Sandusky County | Zone 2 | 630 | 5.0 | 59.2% |
| Scioto County | Zone 2 | 48 | 2.7 | 37% |
| Seneca County | Zone 1 | 511 | 4.9 | 58.9% |
| Shelby County | Zone 1 | 206 | 5.2 | 60.1% |
| Stark County | Zone 1 | 3,174 | 4.9 | 60.1% |
| Summit County | Zone 1 | 6,002 | 3.1 | 38.7% |
| Trumbull County | Zone 2 | 377 | 2.9 | 34.6% |
| Tuscarawas County | Zone 1 | 480 | 5.6 | 66.4% |
| Union County | Zone 1 | 968 | 4.8 | 60.2% |
| Van Wert County | Zone 1 | 18 | 4.3 | 53.8% |
| Vinton County | Zone 2 | 4 | 1.9 | 25% |
| Warren County | Zone 1 | 2,076 | 4.2 | 52.5% |
| Washington County | Zone 2 | 290 | 3.1 | 38.1% |
| Wayne County | Zone 1 | 950 | 4.9 | 61.8% |
| Williams County | Zone 2 | 23 | 3.3 | 42.9% |
| Wood County | Zone 2 | 1,469 | 3.5 | 45.5% |
| Wyandot County | Zone 1 | 224 | 3.6 | 46.3% |
Lab tests: buildings tested by radon laboratories, 2008 to 2017; median in pCi/L; “4+ pCi/L” is the share of tests at or above EPA's action level. n/a: no value on file (no tests, or too few to report).
What the zones mean
Zone 1 counties have a predicted average indoor radon screening level above 4 pCi/L, Zone 2 from 2 to 4 pCi/L and Zone 3 below 2 pCi/L. The prediction is from 1993 indoor measurements, geology, aerial radioactivity, soils and foundation types. EPA: “This map should not be used to determine if individual homes need to be tested.” EPA recommends fixing a home at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of exposure.
Buying in Ohio? Order a Ohio title search: owner of record, deeds, mortgages and liens in Cincinnati, Toledo, Delaware, Powell, Dayton, $49 per report.
Radon in Ohio: questions
What radon zone is Ohio?
EPA's 1993 map does not give states one zone; it zones each county. In Ohio, 53 counties are Zone 1, 35 Zone 2 and 0 Zone 3. EPA says the map "should not be used to determine if individual homes need to be tested".
Which Ohio counties have the highest radon levels?
By the share of laboratory tests at or above 4 pCi/L for 2008 to 2017 (counties with 20 or more tests): Pickaway County 81.4% (median 9.5 pCi/L, 154 tests); Fairfield County 76.8% (median 7.4 pCi/L, 1,004 tests); Logan County 73.6% (median 7.9 pCi/L, 487 tests); Delaware County 72.2% (median 6.4 pCi/L, 3,158 tests); Knox County 72% (median 8.1 pCi/L, 987 tests).
How common is high radon in Ohio?
51.6% of the 84,325 tests in the laboratory data for Ohio (2008 to 2017) were at or above 4 pCi/L; the national share was 36.5%. Buildings are tested by choice, often because of a sale or a concern, so the share describes the tests on file, not every home.
Should I test for radon in Ohio?
Yes. EPA recommends testing every home no matter where it is, fixing it at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of radon exposure.
States bordering Ohio
Other free hazard lookups
- Radon by county and ZIP codeEPA radon zone and the radon test results on file for any county, ZIP code or address.
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- Superfund sites near an addressThe nearest EPA Superfund (NPL) sites and their status.
All of these, plus wetlands, FEMA hazard ratings and the federal contamination lists, are in the Environmental Records Report for any US address ($29).
Superfund sites in Ohio · Radon map of every state
Data compiled 2026-10-20. County-level screening information, not a radon measurement of any building.