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 Delaware County, Ohio
EPA puts Delaware County in Zone 1, its highest radon zone, and high results are common there: 72.2% of the 3,730 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
72.2%
19.9 pts above OH
- Delaware
- 72.2%
- Ohio
- 52.3%
3,730 tests, 2008 to 2017
Median result
6.4pCi/L
Action level reached
- Delaware
- 6.4 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
3,730
6th of 79 by tests
- Delaware
- 3,730
- 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
4 of 79
Top quarter
- Delaware
- 72.2%
- Pickaway
- 81.4%
By share, of 79 with 30+ tests
Read a result for Delaware County
Starts at Delaware County's median, 6.4 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 6.4 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. Delaware County's median reported result, 2008 to 2017.
The data
Delaware County, At a glance
Delaware County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Delaware 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 Delaware County, 2008 to 2017, laboratory
Under 2 pCi/L: 11%2 to 4 pCi/L: 17%4 pCi/L and above: 72%
Of 3,730 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 408 | 10.9% |
| 2 to 4 pCi/L | 628 | 16.8% |
| 4 pCi/L and above | 2,694 | 72.2% |
What these figures count
These are the 3,730 tests reported to CDC for Delaware 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).
Delaware County, Compared
Delaware County radon figures, compared
Calculated by Radon411More than half: 72.2% of the 3,730 radon tests reported to CDC for Delaware County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 4th of 79 Ohio counties with 30 or more tests for the same period. That is 19.9 points above the 52.3% pooled from 88 Ohio counties.
The median result, 6.4 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 140.9 pCi/L. The rest split 10.9% under 2 pCi/L and 16.8% from 2 to 4 (Ohio: 23.1% and 24.6%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 72.2% share point the same way here.
No bordering county with a figure for the same period reported a higher share; the closest is Knox County at 72.0%, the lowest Union County at 60.2%. 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 Delaware County went from 2,734 tests (2005 to 2014) to 3,730 (2008 to 2017), the share going from 70.1% to 72.2%.
Nationally, every county with a figure for the same period pools to 35.7%; Delaware County sits 36.5 points above it. CDC also counts 105 tests taken after mitigation in Delaware 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.
Delaware County, Geology
The ground under Delaware County
PredictedUSGS's geologic map puts all of Delaware 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.
Delaware County beside the ground around it
Delaware 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; Franklin County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Delaware County, Local resources
Radon testing and mitigation in Delaware County
Listed radon businesses with an address in Delaware 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: Columbus, Dublin, Delaware, Westerville, Powell, Sunbury, Ostrander, Galena
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
Delaware County, Questions
Questions about radon in Delaware County
Are radon levels high in Delaware County?
Over the 2008 to 2017 laboratory totals, 72.2% of the radon tests reported to CDC for Delaware County, Ohio were at or above 4 pCi/L, and the median reported pre-mitigation result was 6.4 pCi/L. Of 79 Ohio counties with 30 or more tests for the same period, 3 reported a higher share; pooled, the state comes to 52.3%.
Which counties border Delaware County?
Delaware County borders 6 counties: Morrow County, Marion County, Union County, Franklin County, Knox County and Licking County.
Products
Delaware County, Products
Testing a home in Delaware County
In Delaware County, 72.2% of 3,730 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 Delaware 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
MonitorKidde
Radon Detector (RAB) battery digital radon detector with an alarm
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
First reading: Within 12 hours
Short-term kit
Air Chek Short-Term radon test kit you hang, lab fee included
- Lab fee included
In home: 72 to 168 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Delaware County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Delaware County
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Delaware County, Bordering counties
Counties bordering Delaware County
Calculated by Radon411- Radon levels in Knox CountyEPA zone 1
72.0%at or above 4 pCi/L
Median 8.1 pCi/L · 1,530 tests · 0.2 points below Delaware County
- Radon levels in Franklin CountyEPA zone 1
71.9%at or above 4 pCi/L
Median 6.8 pCi/L · 16,142 tests · 0.3 points below Delaware County
- Radon levels in Licking CountyEPA zone 1
71.2%at or above 4 pCi/L
Median 7.0 pCi/L · 4,694 tests · 1.0 points below Delaware County
- Radon levels in Marion CountyEPA zone 1
65.3%at or above 4 pCi/L
Median 6.4 pCi/L · 265 tests · 6.9 points below Delaware County
- Radon levels in Morrow CountyEPA zone 1
65.0%at or above 4 pCi/L
Median 5.7 pCi/L · 177 tests · 7.2 points below Delaware County
- Radon levels in Union CountyEPA zone 1
60.2%at or above 4 pCi/L
Median 4.8 pCi/L · 1,285 tests · 12.0 points below Delaware County
Delaware County, Cities and towns
Cities and towns in Delaware County
Delaware County is growing: the Census Bureau puts it at 242,032 residents on July 1, 2025, up 12.5% from 215,181 in 2020. That works out to 546 people per square mile of land. Columbus, the largest place on its list (938,396 residents in all), extends beyond Delaware County, so no share of the total is worked out for it. Testing is reported here more often than across the state: CDC's 3,730 reported tests for 2008 to 2017 come to 15.4 for every 1,000 residents (2025 estimate), against 8.3 for Ohio.
From Columbus to Shawnee Hills, CDC publishes no figure by town: each reads Delaware County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Columbusextends beyond Delaware County | 938,396 | +3.5% | Counted whole |
| Dublinextends beyond Delaware County | 49,094 | −0.5% | Counted whole |
| Delaware | 46,636 | +11.9% | 19.3% |
| Westervilleextends beyond Delaware County | 38,165 | −2.7% | Counted whole |
| Powell | 18,269 | +28.1% | 7.5% |
| Sunbury | 8,857 | +31.5% | 3.7% |
| Ashley | 1,343 | +11.4% | 0.6% |
| Ostrander | 1,219 | +10.9% | 0.5% |
| Galena | 1,019 | +9.3% | 0.4% |
| Shawnee Hills | 931 | +10.7% | 0.4% |
Places in Delaware County with a city page: 1 of 2
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 Delaware County is counted whole, so it has no share.
Delaware County, Homes
Homes in Delaware County
Of Delaware County's 84,215 homes, 74% are detached houses, against 69% across Ohio; 12% are in buildings of five or more homes. Much of Delaware County is recent building: 49% of its homes have gone up since 2000 and the middle year built is 1999, against 1970 for Ohio. Owners live in 78% of the occupied homes (Ohio: 67%), so for most households a test and a fix are their own to order.
| Homes | Delaware County | Ohio |
|---|---|---|
| Housing units | 84,215 | 5,271,573 |
| Detached houses | 74% | 69% |
| In buildings of 5 or more | 12% | 15% |
| Mobile homes | 2% | 4% |
| Built before 1960 | 11% | 38% |
| Built since 2000 | 49% | 16% |
| Middle year built | 1999 | 1970 |
| Owner-occupied | 78% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.