Short-term kit
PicoCan short-term charcoal canister radon test
- Lab fee included
Method: Charcoal
In home: 48 to 96 hours
Locations and reports
Radon Levels in Williams County, Ohio
EPA puts Williams County in Zone 2, its middle radon zone, and only 28 radon tests from it are on file with CDC (2008 to 2017, laboratory totals). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Highest bordering
61.8%
Henry County
- Henry
- 61.8%
- Fulton
- 45.2%
6 of 6 neighbours have 30+ tests, 2008 to 2017
Nearest county
48.6%
Defiance County, 17 miles
- Defiance
- 48.6%
- Ohio
- 52.3%
Share at 4+ pCi/L, 70 tests, 2008 to 2017
Ground above low
100.0%
0.1 pts above Ohio
- Williams
- 100.0%
- Ohio
- 99.9%
Share of land USGS rates moderate or high potential
Tests reported
28
Too few for a share
- Williams
- 28
- Needed
- 30
2008 to 2017, laboratory
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
EPA predicts 2 to 4 pCi/L indoors
Read a result for Williams County
Starts at EPA's action level
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 4.0 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.
The data
Williams County, At a glance
Williams County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Williams County is a
USGS geologic potential: High across 90% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Williams County, 2008 to 2017, laboratory
CDC holds 28 reported tests for Williams County over the 2008 to 2017 laboratory totals, with a median of 3.3 pCi/L: too few to describe a county (Radon411 reads a share from 30 tests up). Williams County beside the counties around it is how this page reads it.
What these figures count
Only 28 tests were reported to CDC for Williams County over 2008 to 2017 (laboratory totals), and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor this house.
Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).
Williams County, Compared
Williams County radon figures, compared
Calculated by Radon411CDC's largest figure for Williams County rests on 28 tests over the 2008 to 2017 laboratory totals, 12 of them at or above 4 pCi/L, so each test moves its share by 3.6 points and no rank or comparison is drawn from it. Results reached as high as 13.8 pCi/L, with a middle value of 3.3 pCi/L.
Of the counties bordering it, 6 have a figure over the 2008 to 2017 laboratory totals: Henry County reported the largest share at or above 4 pCi/L, 61.8%, and Fulton County the smallest, 45.2%, with DeKalb County, IN at 56.6%, Steuben County, IN at 55.7% and Hillsdale County, MI at 54.8% between. Farther out, Putnam County (44 miles away) at 59.6%, Lucas County (48 miles away) at 40.2% and Wood County (52 miles away) at 45.5% have figures too. Pooled across 88 Ohio counties, 52.3% of reported tests reached that level; across every county in the country with a figure, 35.7%.
Statewide for the same period, Pickaway County reported the highest share (81.4%) and Cuyahoga County the lowest (21.7%). EPA's 1993 map puts Williams County in Zone 2, its middle label: a predicted county average between 2 and 4 pCi/L. USGS geology rates 90% of the county's land high radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Williams County, Geology
The ground under Williams County
PredictedMost of the ground under Williams County is one class on USGS's geologic map: 90.3% of its land is high radon potential, with 9.7% moderate. The map puts 90.3% of Williams County in the area it calls Till Plains and 9.7% in Lake Plains. USGS gives the first a radon index of 14, in the high band (12 to 17), and the second 10, in the moderate band (9 to 11).
| 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 | 90.3% |
| Lake Plains | Glacial lake deposits, Devonian shale and limestone. | Moderate | 10 | 9.7% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Williams County beside the ground around it
Williams County has more high-potential ground than Ohio as a whole: 90.3% of its land against 62.8%. Of the 6 counties that border it, 3 have more high-potential ground, Hillsdale County, MI the most at 100%.
The map rates the ground, not the air in any home.
Local help
Williams County, Local resources
Radon testing and mitigation in Williams 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.
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
Williams County, Questions
Questions about radon in Williams County
Are radon levels high in Williams County?
Over the 2008 to 2017 laboratory totals, 42.9% of the radon tests reported to CDC for Williams County, Ohio were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.3 pCi/L. Of the counties bordering it, 6 have a figure over the 2008 to 2017 laboratory totals: Henry County reported the largest share at or above 4 pCi/L, 61.8%, and Fulton County the smallest, 45.2%, with DeKalb County, IN at 56.6%, Steuben County, IN at 55.7% and Hillsdale County, MI at 54.8% between.
Which counties border Williams County?
Williams County borders 6 counties: Defiance County, OH, Steuben County, IN, Hillsdale County, MI, Fulton County, OH, DeKalb County, IN and Henry County, OH.
Products
Williams County, Products
Testing a home in Williams County
No CDC figure names Williams County; the nearest county with one, Defiance County (17 miles away), reported 48.6% of its tests at or above 4 pCi/L over the 2008 to 2017 laboratory totals, the only reading nearby until a test of this home. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Williams County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
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
Monitor
RM-65 rechargeable radon detector with a color screen and alarm
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
First reading: Within 6 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Williams County, Bordering counties
Counties bordering Williams County
Calculated by Radon411- Radon levels in Henry County, OHEPA zone 2
61.8%at or above 4 pCi/L
Median 5.3 pCi/L · 34 tests
- Radon levels in DeKalb County, INEPA zone 1
56.6%at or above 4 pCi/L
Median 4.4 pCi/L · 242 tests
- Radon levels in Steuben County, INEPA zone 1
55.7%at or above 4 pCi/L
Median 4.5 pCi/L · 140 tests
- Radon levels in Hillsdale County, MIEPA zone 1
54.8%at or above 4 pCi/L
Median 4.4 pCi/L · 2,086 tests
- Radon levels in Defiance County, OHEPA zone 2
48.6%at or above 4 pCi/L
Median 3.8 pCi/L · 70 tests
- Radon levels in Fulton County, OHEPA zone 2
45.2%at or above 4 pCi/L
Median 3.1 pCi/L · 62 tests
Williams County, Cities and towns
Cities and towns in Williams County
About 36,549 people live in Williams County by the Census Bureau's estimate for July 1, 2025, 535 fewer than in 2020 (−1.4%). That works out to 87 people per square mile of land. Its largest town, Bryan, has 8,579 residents, 23.5% of the total. Together its 9 incorporated places hold 53.8% of those residents; the other 46.2% live outside any of them. Reported testing is thin here: 28 tests over 2008 to 2017, or 0.8 for every 1,000 residents (2025 estimate), where Ohio as a whole comes to 8.3.
From Bryan to Holiday City, CDC publishes no figure by town: each reads Williams County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Bryan | 8,579 | −1.6% | 23.5% |
| Montpelier | 3,884 | −1.3% | 10.6% |
| Edgerton | 1,882 | +0.1% | 5.1% |
| West Unity | 1,735 | −1.1% | 4.7% |
| Pioneer | 1,419 | −1.1% | 3.9% |
| Stryker | 1,239 | −1.7% | 3.4% |
| Edon | 784 | −0.3% | 2.1% |
| Blakeslee | 105 | −1.9% | 0.3% |
| Holiday City | 47 | −2.1% | 0.1% |
9 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).
Williams County, Homes
Homes in Williams County
Williams County is a place of houses on their own lots: 79% of its 16,574 homes are detached single-family houses, against 69% across Ohio. Half of its homes were built before 1966, close to Ohio's 1970: 43% date from before 1960 and 11% from 2000 or later. Owners live in 76% of the occupied homes (Ohio: 67%), so for most households a test and a fix are their own to order.
| Homes | Williams County | Ohio |
|---|---|---|
| Housing units | 16,574 | 5,271,573 |
| Detached houses | 79% | 69% |
| In buildings of 5 or more | 3% | 15% |
| Mobile homes | 8% | 4% |
| Built before 1960 | 43% | 38% |
| Built since 2000 | 11% | 16% |
| Middle year built | 1966 | 1970 |
| Owner-occupied | 76% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.