Updated November 2026 · Data: CDC National Environmental Public Health Tracking Network (radon test results from laboratories, 2008–2017), EPA Map of Radon Zones · Sources and method
Radon testing laboratories reported 13,807 pre-mitigation radon tests from buildings in Franklin County, Ohio between 2008 and 2017, according to the CDC Tracking Network. 71.9% of those tests were at or above the EPA action level of 4 pCi/L, and the median result was 6.8 pCi/L. More than half of the tested buildings reached the action level. The county’s share of high results is higher than the Ohio figure of 51.6% and above the U.S. figure of 36.4%. Franklin County is in EPA radon Zone 1 (highest potential, predicted average above 4 pCi/L).
These are area results, not your home’s level. Homes next to each other can have very different radon levels. The only way to know yours is to test.
Radon test results in Franklin County
| Test result | Franklin County | Ohio | United States |
|---|---|---|---|
| Below 2 pCi/L | 12.1% | 23.6% | 38.8% |
| 2 to 4 pCi/L | 15.9% | 24.8% | 24.8% |
| 4 pCi/L or higher | 71.9% | 51.6% | 36.4% |
About 12% of tests in Franklin County came back below 2 pCi/L, and 15.9% fell between 2 and 4 pCi/L, where the EPA suggests considering a fix. The average result (9.5 pCi/L) is well above the median (6.8 pCi/L) because a smaller number of very high readings pull the average up; the highest test reported was 244.1 pCi/L.
How Franklin County compares with other Ohio counties
| County | Tests | 4 pCi/L or higher | Median (pCi/L) |
|---|---|---|---|
| Franklin County (this page) | 13,807 | 71.9% | 6.8 |
| Pickaway County | 154 | 81.4% | 9.5 |
| Fairfield County | 1,004 | 76.8% | 7.4 |
| Logan County | 487 | 73.6% | 7.9 |
| Delaware County | 3,158 | 72.2% | 6.4 |
| Knox County | 987 | 72.0% | 8.1 |
| Auglaize County | 113 | 71.2% | 6.5 |
| Licking County | 3,431 | 71.2% | 7.0 |
| Champaign County | 412 | 71.1% | 6.8 |
All Ohio counties, the radon zone map and state contacts: Radon in Ohio.
How to test your home in Franklin County
- The Ohio Department of Health, Radon Education and Licensing Program can tell you about free or discounted test kits and certified professionals (phone: 614-728-0272).
- Short-term test kits take 2 to 4 days. Put the kit in the lowest lived-in level of the home, with windows and doors closed. See how to test for radon.
- If the result is 4 pCi/L or higher, the EPA recommends fixing the home; between 2 and 4 pCi/L, consider a fix. Read what radon level is safe.
- A radon mitigation system usually lowers levels by 80% to 99%. Typical prices are in our radon mitigation cost guide.
Frequently asked questions
Is radon a problem in Franklin County?
71.9% of 13,807 pre-mitigation radon tests in Franklin County from 2008 to 2017 were at or above 4 pCi/L, according to CDC Tracking Network laboratory data. The county is in EPA radon Zone 1. Any home can have high radon, so testing is the only way to know.
What is the average radon level in Franklin County?
The median test result in Franklin County is 6.8 pCi/L and the mean is 9.5 pCi/L (CDC Tracking Network, 2008–2017). For comparison, the average indoor radon level in U.S. homes is about 1.3 pCi/L, according to the EPA.
How does Franklin County compare with the rest of Ohio?
Franklin County ranks 6 of 80 Ohio counties (with at least 20 tests) by the share of tests at or above 4 pCi/L. Statewide, 51.6% of 84,325 laboratory tests reached that level.
Should I test if my neighbor’s result was low?
Yes. Radon depends on the soil and rock under each building and on how the building is built, so two houses on the same street can have very different results.
Sources and method
The CDC National Environmental Public Health Tracking Network collects radon test results from radon testing laboratories and summarizes them by county over 10-year periods; the latest period available is 2008–2017. Numbers describe buildings that were tested (mostly homes tested by their owners), not a random sample of every home, and counties with few tests are less reliable. We only publish county pages where at least 100 buildings were tested. State and U.S. figures on this page are weighted by the number of tests in each county. Data retrieved in November 2026.
- CDC Tracking Network Data Explorer: Radon Tests from Labs (median, mean, maximum, number of buildings tested and percent by level, 2008–2017)
- CDC: Radon Testing data
- U.S. EPA: EPA Map of Radon Zones (June 2024 data file)
- Ohio Department of Health, Radon Education and Licensing Program