Central Ohio radon by county and ZIP code
Every county in the Columbus region sits in EPA Radon Zone 1, the tier where the predicted average indoor screening level is above 4 pCi/L, on the EPA's Ohio zone map. The map dates from 1993, and the EPA is blunt that it cannot tell you whether a particular house needs a test. Every house does.
Two sets of county numbers put the zone in context. The 1988-89 EPA and Ohio residential survey, published in the USGS geologic radon assessment of Ohio, used two-to-seven-day charcoal tests on the lowest level of each home; its samples were small, so read them as direction rather than precision. The American Lung Association's 2022 analysis of CDC tracking data covers 2008 to 2017 and is far larger for Franklin County. The Ohio Department of Health also keeps a live ZIP and county dashboard built from results reported by Ohio-licensed professionals, and says its maps are for education only.
ZIP-level figures live on that ODH dashboard, which updates monthly, so we have not copied them here. The ZIP rows instead describe the housing and the local detail that shapes how a test and a system should be planned in Columbus and the towns around it.
| County or ZIP | County and EPA zone | What the data and the housing say |
|---|---|---|
| Franklin County | Zone 1 | 1988-89 survey: 170 homes, median 5.4 pCi/L, 64% above 4. 2008-2017: 16,142 pre-mitigation tests, estimated mean 9.5 pCi/L (ALA analysis of CDC data). Sits over the north-south Ohio Shale outcrop band. |
| Delaware County | Zone 1 | 1988-89 survey: 20 homes, median 5.6 pCi/L, 55% above 4. The Delaware Public Health District points residents to free ODH test kits. |
| Licking County | Zone 1 | 1988-89 survey: 29 homes, median 5.3 pCi/L, 72% above 4. Highest testing rate in Ohio for 2008-2017, about 66 tests per 1,000 housing units. |
| Fairfield County | Zone 1 | 1988-89 survey: 31 homes, median 8.1 pCi/L, 61% above 4, with one home at 238.5 pCi/L. |
| Union County | Zone 1 | 1988-89 survey: only 6 homes, none above 4. Far too few to reassure anyone; the EPA still maps Union as Zone 1. |
| Madison County | Zone 1 | 1988-89 survey: 10 homes, median 1.6 pCi/L, 20% above 4. Another small sample; Zone 1 on the EPA map. |
| Pickaway County | Zone 1 | 1988-89 survey: 7 homes, median 4.6 pCi/L, 57% above 4. |
| 43206 German Village | Franklin / Zone 1 | 1800s brick homes on tight lots. Discharge must clear openings into the house next door by 10 feet, which often sends the pipe up to the roof. |
| 43214 Clintonville | Franklin / Zone 1 | Mostly 1910s to 1940s homes, many with stone or block walls and patched floors. Plan for extra sealing and a communication test before choosing the suction point. |
| 43209 Bexley | Franklin / Zone 1 | Period revival homes with full basements and mature landscaping. Interior chases are common where an outside run would pass windows or a patio. |
| 43212 Grandview Heights | Franklin / Zone 1 | Dense early 20th century streets. Close side yards make the 10-foot rule around neighbors' openings a real routing limit. |
| 43221 Upper Arlington | Franklin / Zone 1 | Period revival and mid-century homes, many with finished basements. Test before and after any lower-level renovation. |
| 43085 Worthington | Franklin / Zone 1 | Historic village core plus postwar and later neighborhoods. Basements with sumps need an airtight cover that can still be lifted for pump service. |
| 43213 Whitehall | Franklin / Zone 1 | Postwar ranches on slabs, crawls, and partial basements. Ohio's protocol calls for a test on each foundation type. |
| 43068 Reynoldsburg | Franklin, Licking, Fairfield / Zone 1 | Ranches plus later subdivisions across three counties. Mixed slab-and-crawl foundations are common. |
| 43230 Gahanna | Franklin / Zone 1 | Mid-century and newer homes along Big Walnut Creek. The USGS found sand and gravel valley deposits let soil gas move more freely than clay till. |
| 43081 Westerville | Franklin, Delaware / Zone 1 | Uptown's older homes plus decades of subdivisions. Split-levels with lower rec rooms deserve a test on that level. |
| 43026 Hilliard | Franklin / Zone 1 | Subdivisions with split-levels that combine a basement and a crawl. One fan can often serve both if the design allows. |
| 43017 Dublin | Franklin, Delaware, Union / Zone 1 | Mostly 1970s to 2020s construction. Some homes have a builder's passive pipe that only needs a fan if the test is 4 or higher. |
| 43054 New Albany | Franklin, Licking / Zone 1 | Large newer homes, some with more than one foundation area, and more new construction east toward the Intel site. |
| 43123 Grove City | Franklin / Zone 1 | Mid-century neighborhoods and newer subdivisions south of Columbus. Poured basements and slabs are the common cases. |
| 43110 Canal Winchester | Franklin, Fairfield / Zone 1 | Village core plus fast-growing subdivisions. Test new homes as soon as possible after move-in, as the EPA advises. |
| 43065 Powell | Delaware / Zone 1 | Mostly 1990s and newer. Where a passive pipe exists, check that it actually exits the roof rather than ending in the attic. |
| 43035 Lewis Center | Delaware / Zone 1 | Delaware County growth corridor of newer subdivisions. Activating a passive pipe is licensed mitigation work in Ohio. |
| 43015 Delaware | Delaware / Zone 1 | County seat with an older downtown and new neighborhoods around it. A study cited by the USGS found higher basement radon over the Columbus and Delaware limestones than over nearby shale. |
| 43021 Galena and 43074 Sunbury | Delaware / Zone 1 | Rural lots around Hoover Reservoir and Big Walnut Creek, many on private wells. Test the air first, then decide about the water. |
| 43023 Granville | Licking / Zone 1 | College-village homes of many eras, with private wells on the rural edges. Ohio's well rules set no radon limit, so water tests happen only on request. |
| 43062 Pataskala and 43031 Johnstown | Licking / Zone 1 | Older village homes plus new subdivisions tied to growth around the Intel site. New homes should be tested soon after occupancy. |
| 43147 Pickerington | Fairfield, Franklin / Zone 1 | Mostly 1990s and newer subdivisions. Fairfield had the region's highest median in the 1988-89 survey. |
| 43130 Lancaster | Fairfield / Zone 1 | County seat with older homes downtown. Stone and block basements call for thorough sealing alongside suction. |
| 43040 Marysville and 43064 Plain City | Union, Madison / Zone 1 | Newer subdivisions around town, farmland and private wells beyond. Small historical samples say little; only a test says anything about your house. |
The next step is the same in every row. Test the lowest level people actually use, following Ohio's placement rules, during the heating season if you can. Ohio homeowners can order a free kit through ohio.radon.com, and a home sale calls for an Ohio-licensed tester running at least 48 hours. A result of 4 pCi/L or more means fix the home; between 2 and 4, the EPA recommends considering it.
For the geology behind these numbers, read our Ohio Shale explainer. For what a fix costs by foundation type, see the pricing guide.
Data sources
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