Ohio · county radon data
Radon in Franklin County, Ohio
71.9% of the 13,807 home radon tests on record here reached the EPA action level — among the higher-testing counties in the state, ranked #6 of 88 tested Ohio counties.
What the numbers say
Franklin County sits 18.1 points above the Ohio median (53.8% of tests over the limit across the state's counties). The median reading among its 13,807 reported tests was 6.8 pCi/L — and the single highest test on record reached 244.1 pCi/L, more than 61× the action level. EPA maps place the county in Radon Zone 1 — its highest-potential category, where average indoor screening levels are predicted above 4 pCi/L.
Why: the ground under Franklin County
Sits over the Devonian Ohio Shale — a uranium-rich black shale running through central Ohio. Where the shale lies near the surface under permeable glacial soils, radon moves readily into homes; it's the reason the Columbus area tests among the highest big-metro radon rates in the country.
Geology sources: USGS WRI 98-4169 · EPA OH zone documentation.
The housing stock factor
The median Franklin County home dates to 1979 — decades before radon-resistant new construction entered building codes. With 1,333,048 residents largely housed in that older stock, testing is the only way any individual household knows where it stands.
ZIP codes in Franklin County
Ohio doesn't publish ZIP-level test results, so these ZIPs share the county figures above — the roster is here so you can confirm your address is covered by this data.
| ZIP | Place |
|---|---|
| 43002 | Amlin |
| 43004 | Blacklick |
| 43016 | Dublin |
| 43017 | Dublin |
| 43026 | Hilliard |
| 43054 | New Albany |
| 43068 | Reynoldsburg |
| 43081 | Westerville |
| 43085 | Columbus |
| 43109 | Brice |
| 43119 | Galloway |
| 43123 | Grove City |
| 43125 | Groveport |
| 43126 | Harrisburg |
| 43201 | Columbus |
| 43202 | Columbus |
| 43203 | Columbus |
| 43204 | Columbus |
| 43205 | Columbus |
| 43206 | Columbus |
| 43207 | Columbus |
| 43209 | Columbus |
| 43210 | Columbus |
| 43211 | Columbus |
| 43212 | Columbus |
| 43213 | Columbus |
| 43214 | Columbus |
| 43215 | Columbus |
| 43217 | Columbus |
| 43218 | Columbus |
| 43219 | Columbus |
| 43220 | Columbus |
| 43221 | Columbus |
| 43222 | Columbus |
| 43223 | Columbus |
| 43224 | Columbus |
| 43227 | Columbus |
| 43228 | Columbus |
| 43229 | Columbus |
| 43230 | Columbus |
| 43231 | Columbus |
| 43232 | Columbus |
| 43235 | Columbus |
Franklin County in the Ohio picture
| Franklin County | 71.9% over the limit | 13,807 tests |
| Ohio's highest: Pickaway County | 81.4% | 154 tests |
| Ohio county median | 53.8% | 88 counties ranked |
| Share of all Ohio tests from this county | 16.4% | |
Ranked nearby in Ohio
- Logan County — #3, 73.6% of 487 tests over the limit
- Delaware County — #4, 72.2% of 3,158 tests over the limit
- Knox County — #5, 72% of 987 tests over the limit
- Auglaize County — #7, 71.2% of 113 tests over the limit
- Licking County — #8, 71.2% of 3,431 tests over the limit
- Champaign County — #9, 71.1% of 412 tests over the limit
(Ranking neighbors — counties adjacent in the Ohio test ranking, not necessarily on the map.)
High test? Fixes and real pricing: the Ohio mitigation cost guide. Every statistic here traces to the methodology (CDC EPHT (labs), 2008–2017; zones: EPA; year built & population: ACS 5-year).
Franklin County radon FAQ
- Is radon high in Franklin County?
- 71.9% of 13,807 home tests reported to the CDC came back at or above the EPA action level of 4 pCi/L — 18.1 points above the Ohio county median of 53.8%, ranking #6 of 88 tested counties. EPA classifies the county as Zone 1.
- Does an older home in Franklin County mean more radon risk?
- The county's median home was built in 1979 — before radon-resistant construction practices entered building codes in the 1990s, so most of the housing stock has no built-in radon protection. Construction age changes the odds, not the answer: only a test tells you about your house.
- Where do these Franklin County numbers come from?
- 13,807 aggregated home tests in the CDC's Environmental Public Health Tracking dataset (CDC EPHT 2008-2017). Median reading: 6.8 pCi/L; the highest recorded test hit 244.1 pCi/L. How we handle the data, including its limits, is documented on our methodology page.
- What's the highest radon reading recorded in Franklin County?
- 244.1 pCi/L — 61× the EPA action level — against a county median of 6.8 pCi/L across 13,807 tests. That spread is the point: neighboring homes routinely test wildly differently.