Short-term kit
RA100 short-term liquid scintillation radon test kit
- Lab fee extra
Method: Liquid scintillation
In home: 48 to 96 hours
Locations and reports
Radon Levels in Onslow County, North Carolina
EPA puts Onslow County in Zone 3, its lowest radon zone, and only 4 radon tests from it are on file with CDC (2020). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Share at 4+ pCi/L
2.7%
19.9 pts below NC
- Onslow
- 2.7%
- NC
- 22.6%
188 tests, 2008 to 2017
Median result
0.5pCi/L
Below action level
- Onslow
- 0.5 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
188
49th of 75 by tests
- Onslow
- 188
- Wake
- 9,694
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 3
Lower potential
- 1
- 2
- Zone 3
1 highest, 3 lowest
EPA predicts under 2 pCi/L indoors
Rank in NC
65 of 75
Lowest quarter
- Onslow
- 2.7%
- Transylvania
- 47.8%
By share, of 75 with 30+ tests
Read a result for Onslow County
Starts at Onslow County's median, 0.5 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 0.5 pCi/L
Below 2 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is below 2 pCi/L, the level at which EPA says a fix should be considered. Onslow County's median reported result, 2008 to 2017.
The data
Onslow County, At a glance
Onslow County at a glance
Predicted: EPA radon zone
EPA Zone 3: lower predicted potential
USGS geologic potential: Low across 92% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Onslow County, 2020
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 10.0% |
| 2020 | 0.0% |
2020: 0.0%. Across these years the share ran from 0.0% to 10.0%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
Only 4 tests were reported to CDC for Onslow County over 2020, 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: 2020. Measured data period: 2005 to 2020 (every CDC figure on file).
Onslow County, Compared
Onslow County radon figures, compared
Calculated by Radon411Only 5 of 188 radon tests reported for Onslow County over the 2008 to 2017 laboratory totals reached 4 pCi/L (2.7%). The median result, 0.5 pCi/L, sits below 2, well under EPA's 4 pCi/L action level, and the top reported result was 16.1 pCi/L.
The newest figure, in 2020, counts only 4 tests (0.0% at or above 4 pCi/L), too few to compare, so this reading uses the 188-test figure.
Across 99 North Carolina counties pooled together, 22.6% of tests reached that level, so Onslow County runs 19.9 points below its state. Against the national pool of 35.7%, the gap is 33.0 points lower. Its place in the state: 65th of 75 North Carolina counties with 30 or more tests for the same period.
Zone 3 on EPA's map (predicted average under 2 pCi/L) and a 2.7% share point the same way here. Carteret County, the one bordering county with a figure for the same period, reported 0.0%.
Below the action level, 178 tests (94.7%) came in under 2 pCi/L, against 55.6% statewide, and 5 tests (2.7%) fell between 2 and 4, against 21.8% statewide. USGS geology rates 92% of the county's land low radon potential.
The busiest year on file was 2014, with 10 tests reported; the quietest, 2020, had 4.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Onslow County, Geology
The ground under Onslow County
PredictedUSGS's geologic map puts all of Onslow County's mapped land in one class: low radon potential. The map puts 68.6% of Onslow County in the area it calls Inner Coastal Plain and 23.3% in Outer Coastal Plain. USGS gives the first a radon index of 8 and the second 7, both in the low band (5 to 8).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Inner Coastal Plain | Fossiliferous clay and sand, shelly sand, sandy marl, and limestone. | Low | 8 | 68.6% |
| Outer Coastal Plain | Unconsolidated sand. | Low | 7 | 23.3% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Onslow County beside the ground around it
Across North Carolina 1.3% of the land is rated high; none of Onslow County's is. None of the 4 counties that border it has any moderate-potential ground either.
The map rates the ground, not the air in any home.
Local help
Onslow County, Local resources
Radon testing and mitigation in Onslow County
- North Carolina Radon ProgramNorth Carolina Radon Program, run by NCDHHS, answers questions about testing, mitigation and the rules in North Carolina.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsAsk the program whether it has free or discounted kits, or compare kits you can buy.
- Compare kits
- Professionals in North Carolina2 professionals are listed in North Carolina.
What North Carolina's program says
- Licensing of radon professionals
The North Carolina Radon Program is presently developing a Radon Proficiency Program as directed by Session Law 2023-91 House Bill 782 .
What it means
Onslow County, Questions
Questions about radon in Onslow County
Are radon levels high in Onslow County?
In 2020, 0.0% of the radon tests reported to CDC for Onslow County, North Carolina were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.5 pCi/L. Of 75 North Carolina counties with 30 or more tests for the same period, 64 reported a higher share; pooled, the state comes to 22.6%.
Which counties border Onslow County?
Onslow County borders 4 counties: Jones County, Pender County, Duplin County and Carteret County.
Products
Onslow County, Products
Testing a home in Onslow County
In Onslow County, 2.7% of 188 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 22.6% pooled across North Carolina. Zone 3 is the lowest label, yet homes at or above 4 pCi/L occur in every zone: a short-term kit (2 to 90 days) is the quick first check in Onslow County.
Test kits and monitors3
See every kit and monitor
Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Monitor
lüft plug-in radon and indoor air quality monitor
- C-NRPP 2024/25: Approved
- Plug-in
- Wi-Fi, Bluetooth
- App only
First reading: Within 90 minutes
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Onslow County, Bordering counties
Counties bordering Onslow County
Calculated by Radon411- Radon levels in Pender CountyEPA zone 3
11.8%at or above 4 pCi/L
Median 0.1 pCi/L · 17 tests · 9.1 points above Onslow County
- Radon levels in Jones CountyEPA zone 3
0.0%at or above 4 pCi/L
Median 1.8 pCi/L · 1 test · 2.7 points below Onslow County
- Radon levels in Duplin CountyEPA zone 3
0.0%at or above 4 pCi/L
Median 0.1 pCi/L · 5 tests · 2.7 points below Onslow County
- Radon levels in Carteret CountyEPA zone 3
0.0%at or above 4 pCi/L
Median 0.1 pCi/L · 41 tests · 2.7 points below Onslow County
Onslow County, Cities and towns
Cities and towns in Onslow County
Onslow County is growing: the Census Bureau puts it at 217,175 residents on July 1, 2025, up 5.9% from 204,984 in 2020. That works out to 285 people per square mile of land. Its largest town, Jacksonville, has 72,732 residents, 33.5% of the total. Reported testing is thin here: 188 tests over 2008 to 2017, or 0.9 for every 1,000 residents (2025 estimate), where North Carolina as a whole comes to 6.5.
From Jacksonville to North Topsail Beach, CDC publishes no figure by town: each reads Onslow County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Jacksonville | 72,732 | −0.6% | 33.5% |
| Holly Ridge | 5,908 | +39.1% | 2.7% |
| Surf Cityextends beyond Onslow County | 5,142 | +31.9% | Counted whole |
| Swansboro | 4,174 | +11.2% | 1.9% |
| Richlands | 2,485 | +8.5% | 1.1% |
| North Topsail Beach | 1,097 | +8.6% | 0.5% |
6 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). A place that extends beyond Onslow County is counted whole, so it has no share.
Onslow County, Homes
Homes in Onslow County
Of Onslow County's 85,917 homes, 65% are detached houses, against 65% across North Carolina; 12% are mobile homes. Half of its homes were built before 1997, close to North Carolina's 1990: 8% date from before 1960 and 46% from 2000 or later. 61% of occupied homes are lived in by their owner (North Carolina: 66%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Onslow County | North Carolina |
|---|---|---|
| Housing units | 85,917 | 4,815,195 |
| Detached houses | 65% | 65% |
| In buildings of 5 or more | 9% | 14% |
| Mobile homes | 12% | 11% |
| Built before 1960 | 8% | 14% |
| Built since 2000 | 46% | 33% |
| Middle year built | 1997 | 1990 |
| Owner-occupied | 61% | 66% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.