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 Franklin County, Ohio
EPA puts Franklin County in Zone 1, its highest radon zone, and high results are common there: 71.9% of the 16,142 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
71.9%
19.6 pts above OH
- Franklin
- 71.9%
- Ohio
- 52.3%
16,142 tests, 2008 to 2017
Median result
6.8pCi/L
Action level reached
- Franklin
- 6.8 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
16,142
Most tested in Ohio
- 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
6 of 79
Top quarter
- Franklin
- 71.9%
- Pickaway
- 81.4%
By share, of 79 with 30+ tests
Read a result for Franklin County
Starts at Franklin County's median, 6.8 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 6.8 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. Franklin County's median reported result, 2008 to 2017.
The data
Franklin County, At a glance
Franklin County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Franklin 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 Franklin County, 2008 to 2017, laboratory
Under 2 pCi/L: 12%2 to 4 pCi/L: 16%4 pCi/L and above: 72%
Of 16,142 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 1,959 | 12.1% |
| 2 to 4 pCi/L | 2,569 | 15.9% |
| 4 pCi/L and above | 11,614 | 71.9% |
What these figures count
These are the 16,142 tests reported to CDC for Franklin 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).
Franklin County, Compared
Franklin County radon figures, compared
Calculated by Radon411More than half: 71.9% of the 16,142 radon tests reported to CDC for Franklin County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 6th of 79 Ohio counties with 30 or more tests for the same period. That is 19.6 points above the 52.3% pooled from 88 Ohio counties.
The median result, 6.8 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 244.1 pCi/L. The rest split 12.1% under 2 pCi/L and 15.9% from 2 to 4 (Ohio: 23.1% and 24.6%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 71.9% share point the same way here.
3 of its 6 bordering counties with figures ran higher, led by Pickaway County at 81.4%; Union County reported 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 Franklin County went from 12,346 tests (2005 to 2014) to 16,142 (2008 to 2017), the share going from 71.4% to 71.9%.
Nationally, every county with a figure for the same period pools to 35.7%; Franklin County sits 36.2 points above it. CDC also counts 629 tests taken after mitigation in Franklin 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.
Franklin County, Geology
The ground under Franklin County
PredictedUSGS's geologic map puts all of Franklin 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.
Franklin County beside the ground around it
Franklin 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; Delaware County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Franklin County, Local resources
Radon testing and mitigation in Franklin County
Listed radon businesses with an address in Franklin 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, Grove City, Reynoldsburg, Hilliard, Westerville, Gahanna, Pickerington, Worthington, New Albany, Canal Winchester, Groveport
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
Franklin County, Questions
Questions about radon in Franklin County
Are radon levels high in Franklin County?
Over the 2008 to 2017 laboratory totals, 71.9% of the radon tests reported to CDC for Franklin County, Ohio were at or above 4 pCi/L, and the median reported pre-mitigation result was 6.8 pCi/L. Of 79 Ohio counties with 30 or more tests for the same period, 5 reported a higher share; pooled, the state comes to 52.3%.
Which counties border Franklin County?
Franklin County borders 6 counties: Madison County, Pickaway County, Fairfield County, Delaware County, Licking County and Union County.
Products
Franklin County, Products
Testing a home in Franklin County
In Franklin County, 71.9% of 16,142 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 Franklin 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 monitorMonitorSafetySiren
Pro4 plug-in radon detector with a display and alarm
- C-NRPP 2024/25: Not included
- Plug-in
- Alarm
- Screen
First reading: Within 48 hours
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
Franklin County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Franklin County
Explore
Franklin County, Bordering counties
Counties bordering Franklin County
Calculated by Radon411- Radon levels in Pickaway CountyEPA zone 1
81.4%at or above 4 pCi/L
Median 9.5 pCi/L · 183 tests · 9.5 points above Franklin County
- Radon levels in Fairfield CountyEPA zone 1
76.8%at or above 4 pCi/L
Median 7.4 pCi/L · 1,175 tests · 4.9 points above Franklin County
- Radon levels in Delaware CountyEPA zone 1
72.2%at or above 4 pCi/L
Median 6.4 pCi/L · 3,730 tests · 0.3 points above Franklin County
- Radon levels in Licking CountyEPA zone 1
71.2%at or above 4 pCi/L
Median 7.0 pCi/L · 4,694 tests · 0.7 points below Franklin County
- Radon levels in Madison CountyEPA zone 1
67.4%at or above 4 pCi/L
Median 5.7 pCi/L · 549 tests · 4.5 points below Franklin County
- Radon levels in Union CountyEPA zone 1
60.2%at or above 4 pCi/L
Median 4.8 pCi/L · 1,285 tests · 11.7 points below Franklin County
Franklin County, Cities and towns
Cities and towns in Franklin County
The Census Bureau estimates 1,361,536 residents in Franklin County for July 1, 2025, 37,058 more than in 2020 (+2.8%). Packed into its land, that is 2,557 people per square mile. Columbus, the largest place on its list (938,396 residents in all), extends beyond Franklin County, so no share of the total is worked out for it. CDC's 16,142 reported tests for 2008 to 2017 work out to 11.9 per 1,000 residents (2025 estimate), close to Ohio's 8.3.
From Columbus to Brice, CDC publishes no figure by town: each reads Franklin County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Columbusextends beyond Franklin County | 938,396 | +3.5% | Counted whole |
| Dublinextends beyond Franklin County | 49,094 | −0.5% | Counted whole |
| Grove City | 45,180 | +9.3% | 3.3% |
| Reynoldsburgextends beyond Franklin County | 43,350 | +5.6% | Counted whole |
| Hilliard | 38,898 | +4.6% | 2.9% |
| Westervilleextends beyond Franklin County | 38,165 | −2.7% | Counted whole |
| Gahanna | 35,986 | +0.8% | 2.6% |
| Upper Arlington | 35,893 | −2.3% | 2.6% |
| Pickeringtonextends beyond Franklin County | 26,333 | +13.4% | Counted whole |
| Whitehall | 19,805 | −1.5% | 1.5% |
| Worthington | 14,543 | −1.6% | 1.1% |
| Bexley | 12,452 | −10.5% | 0.9% |
Places in Franklin County with a city page: 1 of 2
- New Albany (part)
- Canal Winchester (part)
- Grandview Heights
- Obetz
- Groveport
- Lithopolis (part)
- Minerva Park
- Urbancrest
- Marble Cliff
- Valleyview
- Riverlea
- Harrisburg (part)
- Lockbourne (part)
- Brice
26 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. “(part)” marks a place that extends into another county. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond Franklin County is counted whole, so it has no share.
Franklin County, Homes
Homes in Franklin County
Fewer than six in ten of Franklin County's 588,892 homes are detached houses (53%, against 69% across Ohio); the rest are attached, in shared buildings or mobile. Much of Franklin County is recent building: 22% of its homes have gone up since 2000 and the middle year built is 1979, against 1970 for Ohio. 53% 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 | Franklin County | Ohio |
|---|---|---|
| Housing units | 588,892 | 5,271,573 |
| Detached houses | 53% | 69% |
| In buildings of 5 or more | 25% | 15% |
| Mobile homes | 1% | 4% |
| Built before 1960 | 26% | 38% |
| Built since 2000 | 22% | 16% |
| Middle year built | 1979 | 1970 |
| Owner-occupied | 53% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.