Long-term kit
RL416 long-term radon test kit, lab fee included
- Lab fee included
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Clark County, Ohio
EPA puts Clark County in Zone 1, its highest radon zone, and high results are common there: 57.5% of the 1,447 radon tests reported to CDC (2008 to 2017, laboratory totals) came back at or above 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Share at 4+ pCi/L
57.5%
5.2 pts above OH
- Clark
- 57.5%
- Ohio
- 52.3%
1,447 tests, 2008 to 2017
Median result
4.9pCi/L
Action level reached
- Clark
- 4.9 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
1,447
19th of 79 by tests
- Clark
- 1,447
- Franklin
- 16,142
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in Ohio
35 of 79
Middle half
- Clark
- 57.5%
- Pickaway
- 81.4%
By share, of 79 with 30+ tests
Read a result for Clark County
Starts at Clark County's median, 4.9 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 4.9 pCi/L
At or above 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Clark County's median reported result, 2008 to 2017.
The data
Clark County, At a glance
Clark County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Clark County in
USGS geologic potential: High across 100% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Clark County, 2008 to 2017, laboratory
Under 2 pCi/L: 22%2 to 4 pCi/L: 21%4 pCi/L and above: 57%
Of 1,447 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 314 | 21.7% |
| 2 to 4 pCi/L | 301 | 20.8% |
| 4 pCi/L and above | 832 | 57.5% |
What these figures count
These are the 1,447 tests reported to CDC for Clark County over 2008 to 2017 (laboratory totals), many from homes being sold or already suspected of a problem: they describe the county's reported tests, not this house.
Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).
Clark County, Compared
Clark County radon figures, compared
Calculated by Radon411More than half: 57.5% of the 1,447 radon tests reported to CDC for Clark County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 35th of 79 Ohio counties with 30 or more tests for the same period. That is 5.2 points above the 52.3% pooled from 88 Ohio counties.
The median result, 4.9 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 262.7 pCi/L. The rest split 21.7% under 2 pCi/L and 20.8% from 2 to 4 (Ohio: 23.1% and 24.6%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 57.5% share point the same way here.
4 of its 5 bordering counties with figures ran higher, led by Champaign County at 71.1%; Montgomery County reported 50.3%. Statewide for the same period, Pickaway County reported the highest share (81.4%) and Cuyahoga County the lowest (21.7%).
CDC's ten-year totals for Clark County went from 2,026 tests (2005 to 2014) to 1,447 (2008 to 2017), the share going from 56.5% to 57.5%.
Nationally, every county with a figure for the same period pools to 35.7%; Clark County sits 21.8 points above it. CDC also counts 45 tests taken after mitigation in Clark County for the same period: tests in homes where a fix was already in.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Clark County, Geology
The ground under Clark County
PredictedUSGS's geologic map puts all of Clark County's mapped land in one class: high radon potential. All of it lies in the area the map calls Till Plains, to which USGS gives a radon index of 14, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Till Plains | Glacial deposits underlain by Ordovician through Devonian limestone and shale. | High | 14 | 100% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Clark County beside the ground around it
Clark County has more high-potential ground than Ohio as a whole: 100% of its land against 62.8%. Of the 5 counties that border it, none has as large a share of high-potential ground; Champaign County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Clark County, Local resources
Radon testing and mitigation in Clark County
Listed radon businesses with an address in Clark County:
- Radon Education and Licensing ProgramRadon Education and Licensing Program, run by Ohio Department of Health, licenses or certifies radon professionals and offers free or discounted test kits, and answers questions about testing and mitigation in Ohio.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Free radon test kits are available for Ohio homeowners.
- Compare kits
- Professionals in Ohio479 professionals are listed in Ohio.
Listed radon professionals by town: Springfield
What Ohio's program says
- Phone
- 614-728-0272
- indoor.radon@odh.ohio.gov
- Licensing of radon professionals
This program licenses companies and persons directly involved with the radon testing and mitigation industry.
What it means
Clark County, Questions
Questions about radon in Clark County
Are radon levels high in Clark County?
Over the 2008 to 2017 laboratory totals, 57.5% of the radon tests reported to CDC for Clark County, Ohio were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.9 pCi/L. Of 79 Ohio counties with 30 or more tests for the same period, 34 reported a higher share; pooled, the state comes to 52.3%.
Which counties border Clark County?
Clark County borders 5 counties: Champaign County, Greene County, Madison County, Miami County and Montgomery County.
Products
Clark County, Products
Testing a home in Clark County
In Clark County, 57.5% of 1,447 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 52.3% pooled across Ohio. In Zone 1 the year-round level in Clark County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.
Test kits and monitors3
See every kit and monitor
Monitor
View Radon Wi-Fi radon monitor with an e-paper display
- C-NRPP 2024/25: Approved
- Battery
- Wi-Fi, Bluetooth
- Screen, app
Method: Alpha spectrometry
Readings: Every 60 minutes
Short-term kit
Radon Short Term Test Kit short-term charcoal radon test kit, lab fee included
- Lab fee included
Method: Charcoal
In home: 2 to 7 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Clark County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Clark County
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Clark County, Bordering counties
Counties bordering Clark County
Calculated by Radon411- Radon levels in Champaign CountyEPA zone 1
71.1%at or above 4 pCi/L
Median 6.8 pCi/L · 596 tests · 13.6 points above Clark County
- Radon levels in Madison CountyEPA zone 1
67.4%at or above 4 pCi/L
Median 5.7 pCi/L · 549 tests · 9.9 points above Clark County
- Radon levels in Miami CountyEPA zone 1
65.2%at or above 4 pCi/L
Median 6.1 pCi/L · 690 tests · 7.7 points above Clark County
- Radon levels in Greene CountyEPA zone 1
58.6%at or above 4 pCi/L
Median 4.9 pCi/L · 2,602 tests · 1.1 points above Clark County
- Radon levels in Montgomery CountyEPA zone 1
50.3%at or above 4 pCi/L
Median 4.0 pCi/L · 2,922 tests · 7.2 points below Clark County
Clark County, Cities and towns
Cities and towns in Clark County
Clark County's population has barely moved since 2020: 135,340 residents on July 1, 2025 against 135,888 then, by the Census Bureau's estimates. That works out to 341 people per square mile of land. Its largest town, Springfield, has 58,281 residents, 43.1% of the total. CDC's 1,447 reported tests for 2008 to 2017 work out to 10.7 per 1,000 residents (2025 estimate), close to Ohio's 8.3.
From Springfield to Clifton, CDC publishes no figure by town: each reads Clark County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Springfield | 58,281 | −0.5% | 43.1% |
| New Carlisle | 5,525 | −0.6% | 4.1% |
| Enon | 2,456 | −0.4% | 1.8% |
| South Charleston | 1,698 | −0.5% | 1.3% |
| North Hampton | 461 | −1.1% | 0.3% |
| South Vienna | 405 | −1.0% | 0.3% |
| Tremont City | 346 | −1.7% | 0.3% |
| Donnelsville | 257 | −1.2% | 0.2% |
| Catawba | 244 | Level | 0.2% |
| Cliftonextends beyond Clark County | 137 | +2.2% | Counted whole |
10 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond Clark County is counted whole, so it has no share.
Clark County, Homes
Homes in Clark County
Of Clark County's 61,092 homes, 74% are detached houses, against 69% across Ohio; 10% are in buildings of five or more homes. Half of its homes were built before 1963, close to Ohio's 1970: 46% date from before 1960 and 8% from 2000 or later. 69% of occupied homes are lived in by their owner (Ohio: 67%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Clark County | Ohio |
|---|---|---|
| Housing units | 61,092 | 5,271,573 |
| Detached houses | 74% | 69% |
| In buildings of 5 or more | 10% | 15% |
| Mobile homes | 4% | 4% |
| Built before 1960 | 46% | 38% |
| Built since 2000 | 8% | 16% |
| Middle year built | 1963 | 1970 |
| Owner-occupied | 69% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.