Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Mercer County, Ohio
EPA puts Mercer County in Zone 1, its highest radon zone, and high results are common there: 57.7% of the 149 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
57.7%
5.4 pts above OH
- Mercer
- 57.7%
- Ohio
- 52.3%
149 tests, 2008 to 2017
Median result
5.1pCi/L
Action level reached
- Mercer
- 5.1 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
149
58th of 79 by tests
- Mercer
- 149
- 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
34 of 79
Middle half
- Mercer
- 57.7%
- Pickaway
- 81.4%
By share, of 79 with 30+ tests
Read a result for Mercer County
Starts at Mercer County's median, 5.1 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 5.1 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. Mercer County's median reported result, 2008 to 2017.
The data
Mercer County, At a glance
Mercer County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Mercer 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 Mercer County, 2008 to 2017, laboratory
Under 2 pCi/L: 21%2 to 4 pCi/L: 21%4 pCi/L and above: 58%
Of 149 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 31 | 20.8% |
| 2 to 4 pCi/L | 32 | 21.5% |
| 4 pCi/L and above | 86 | 57.7% |
What these figures count
These are the 149 tests reported to CDC for Mercer 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).
Mercer County, Compared
Mercer County radon figures, compared
Calculated by Radon411More than half: 57.7% of the 149 radon tests reported to CDC for Mercer County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 34th of 79 Ohio counties with 30 or more tests for the same period. That is 5.4 points above the 52.3% pooled from 88 Ohio counties.
The median result, 5.1 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 48.9 pCi/L. The rest split 20.8% under 2 pCi/L and 21.5% from 2 to 4 (Ohio: 23.1% and 24.6%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 57.7% share point the same way here.
3 of its 4 bordering counties with figures ran higher, led by Auglaize County at 71.2%; Adams County, IN reported 48.5%. 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 Mercer County went from 219 tests (2005 to 2014) to 149 (2008 to 2017), the share going from 56.6% to 57.7%.
Nationally, every county with a figure for the same period pools to 35.7%; Mercer County sits 22.0 points above it.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Mercer County, Geology
The ground under Mercer County
PredictedUSGS's geologic map puts all of Mercer 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.
Mercer County beside the ground around it
Mercer County has more high-potential ground than Ohio as a whole: 100% of its land against 62.8%. Of the 6 counties that border it, none has as large a share of high-potential ground; Adams County, IN comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Mercer County, Local resources
Radon testing and mitigation in Mercer County
Listed radon businesses with an address in Mercer 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: Celina
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
Mercer County, Questions
Questions about radon in Mercer County
Are radon levels high in Mercer County?
Over the 2008 to 2017 laboratory totals, 57.7% of the radon tests reported to CDC for Mercer County, Ohio were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.1 pCi/L. Of 79 Ohio counties with 30 or more tests for the same period, 33 reported a higher share; pooled, the state comes to 52.3%.
Which counties border Mercer County?
Mercer County borders 6 counties: Jay County, IN, Darke County, OH, Auglaize County, OH, Shelby County, OH, Van Wert County, OH and Adams County, IN.
Products
Mercer County, Products
Testing a home in Mercer County
In Mercer County, 57.7% of 149 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 Mercer 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
lüft plug-in radon and indoor air quality monitor
- C-NRPP 2024/25: Approved
- Plug-in
- Wi-Fi, Bluetooth
- App only
First reading: Within 90 minutes
Short-term kitempowerDX
Standard Radon Test short-term mail-in radon test kit
- Lab fee included
Method: Passive sampler
In home: 48 to 96 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Mercer County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Mercer County
Explore
Mercer County, Bordering counties
Counties bordering Mercer County
Calculated by Radon411- Radon levels in Auglaize County, OHEPA zone 1
71.2%at or above 4 pCi/L
Median 6.5 pCi/L · 139 tests · 13.5 points above Mercer County
- Radon levels in Darke County, OHEPA zone 1
63.7%at or above 4 pCi/L
Median 5.6 pCi/L · 270 tests · 6.0 points above Mercer County
- Radon levels in Shelby County, OHEPA zone 1
60.1%at or above 4 pCi/L
Median 5.2 pCi/L · 248 tests · 2.4 points above Mercer County
- Radon levels in Van Wert County, OHEPA zone 1
53.8%at or above 4 pCi/L
Median 4.3 pCi/L · 26 tests · 3.9 points below Mercer County
- Radon levels in Adams County, INEPA zone 1
48.5%at or above 4 pCi/L
Median 3.8 pCi/L · 66 tests · 9.2 points below Mercer County
- Radon levels in Jay County, INEPA zone 1
44.4%at or above 4 pCi/L
Median 2.7 pCi/L · 9 tests · 13.3 points below Mercer County
Mercer County, Cities and towns
Cities and towns in Mercer County
Mercer County's population has barely moved since 2020: 42,737 residents on July 1, 2025 against 42,534 then, by the Census Bureau's estimates. That works out to 92 people per square mile of land. Its largest town, Celina, has 10,936 residents, 25.6% of the total. Reported testing is thin here: 149 tests over 2008 to 2017, or 3.5 for every 1,000 residents (2025 estimate), where Ohio as a whole comes to 8.3.
From Celina to Montezuma, CDC publishes no figure by town: each reads Mercer County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Celina | 10,936 | Level | 25.6% |
| Coldwater | 4,716 | −1.0% | 11.0% |
| St. Henry | 2,624 | +0.7% | 6.1% |
| Fort Recovery | 1,476 | −1.5% | 3.5% |
| Rockford | 1,039 | −1.3% | 2.4% |
| Mendon | 613 | −2.7% | 1.4% |
| Chickasaw | 351 | −1.4% | 0.8% |
| Burkettsvilleextends beyond Mercer County | 266 | −1.8% | Counted whole |
| Montezuma | 149 | −3.2% | 0.3% |
9 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 Mercer County is counted whole, so it has no share.
Mercer County, Homes
Homes in Mercer County
Mercer County is a place of houses on their own lots: 81% of its 18,023 homes are detached single-family houses, against 69% across Ohio. Half of its homes were built before 1974, close to Ohio's 1970: 35% date from before 1960 and 19% from 2000 or later. Owners live in 80% of the occupied homes (Ohio: 67%), so for most households a test and a fix are their own to order.
| Homes | Mercer County | Ohio |
|---|---|---|
| Housing units | 18,023 | 5,271,573 |
| Detached houses | 81% | 69% |
| In buildings of 5 or more | 5% | 15% |
| Mobile homes | 6% | 4% |
| Built before 1960 | 35% | 38% |
| Built since 2000 | 19% | 16% |
| Middle year built | 1974 | 1970 |
| Owner-occupied | 80% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.