Short-term kitempowerDX
Standard Radon Test short-term mail-in radon test kit
- Lab fee included
Method: Passive sampler
In home: 48 to 96 hours
Locations and reports
Radon Levels in New Castle County, Delaware
EPA puts New Castle County in Zone 2, its middle radon zone, and 17.0% of its 10,247 reported radon tests (2008 to 2017, laboratory totals) were at or above 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Share at 4+ pCi/L
17.0%
0.3 pts above DE
- New Castle
- 17.0%
- Delaware
- 16.7%
10,247 tests, 2008 to 2017
Median result
1.8pCi/L
Below action level
- New Castle
- 1.8 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
10,247
Most tested in Delaware
- New Castle
- 10,247
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
EPA predicts 2 to 4 pCi/L indoors
Rank in Delaware
1 of 3
Top quarter
- New Castle
- 17.0%
- New Castle
- 17.0%
By share, of 3 with 30+ tests
Read a result for New Castle County
Starts at New Castle County's median, 1.8 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 1.8 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. New Castle County's median reported result, 2008 to 2017.
The data
New Castle County, At a glance
New Castle County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
New Castle County is a
USGS geologic potential: Moderate across 64% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for New Castle County, 2008 to 2017, laboratory
Under 2 pCi/L: 54%2 to 4 pCi/L: 29%4 pCi/L and above: 17%
Of 10,247 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 5,558 | 54.2% |
| 2 to 4 pCi/L | 2,952 | 28.8% |
| 4 pCi/L and above | 1,737 | 17.0% |
What these figures count
These are the 10,247 tests reported to CDC for New Castle County over 2008 to 2017 (laboratory totals), many from homes being sold or already suspected of a problem: they describe the county's reported tests, not this house.
Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).
New Castle County, Compared
New Castle County radon figures, compared
Calculated by Radon411New Castle County's 10,247 reported tests over the 2008 to 2017 laboratory totals had a middle value of 1.8 pCi/L and a maximum of 45.7 pCi/L, and 17.0% reached 4 pCi/L. Delaware as a whole (3 Delaware counties, pooled) comes to 16.7%: 0.3 points lower than here.
Among its state's counties it ranks 1st of 3 Delaware counties with 30 or more tests for the same period. Statewide for the same period, Kent County reported the highest share (16.9%) and Sussex County the lowest (10.4%).
Below the action level, 5,558 tests (54.2%) came in under 2 pCi/L, against 55.3% statewide, and 2,952 tests (28.8%) fell between 2 and 4, against 28.0% statewide. CDC's ten-year totals for New Castle County went from 7,098 tests (2005 to 2014) to 10,247 (2008 to 2017), the share going from 18.7% to 17.0%.
EPA's 1993 zone map puts New Castle County in Zone 2, a predicted county average between 2 and 4 pCi/L. USGS geology rates 64% of the county's land moderate radon potential.
Next door, the shares run from 16.9% in Kent County to 52.6% in Kent County, MD, with Kent County below New Castle County.
CDC also counts 296 tests taken after mitigation in New Castle County for the same period: tests in homes where a fix was already in.
Pooled shares: Radon411's sum of CDC's county counts for one period.
New Castle County, Geology
The ground under New Castle County
PredictedUSGS's geologic map splits New Castle County: 63.8% of its land is moderate radon potential and 35.7% low. The map puts 42.3% of New Castle County in the area it calls Coastal Plain and 35.6% in Coastal Plain, with one smaller area beside them. USGS gives the first a radon index of 10, in the moderate band (9 to 11), and the second 7, in the low band (5 to 8).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Coastal Plain | Upper Cretaceous and lower Tertiary glauconitic marine sediments. | Moderate | 10 | 42.3% |
| Coastal Plain | Cretaceous, Tertiary and Quaternary quartzitic fluvial and marine sediments. | Low | 7 | 35.6% |
| Piedmont | Gneiss, schist, amphibolite, serpentine, and anorthosite. | Moderate | 11 | 21.5% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
New Castle County beside the ground around it
New Castle County has more moderate-potential ground than Delaware as a whole: 63.8% of its land against 14.0%. Of the 7 counties that border it, 3 have more high-potential ground, Chester County, PA the most at 99.9%.
The map rates the ground, not the air in any home.
Local help
New Castle County, Local resources
Radon testing and mitigation in New Castle County
Listed radon businesses with an address in New Castle County:
- Delaware Division of Public Health Radon OfficeDelaware Division of Public Health Radon Office, run by Delaware Division of Public Health, offers free or discounted test kits, and answers questions about testing and mitigation in Delaware.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Delaware Residents click HERE for your free radon test kit.
- Compare kits
- Professionals in Delaware2 professionals are listed in Delaware.
Listed radon professionals by town: Wilmington
What Delaware's program says
- Phone
- 1-800-464-HELP
What it means
New Castle County, Questions
Questions about radon in New Castle County
Are radon levels high in New Castle County?
Over the 2008 to 2017 laboratory totals, 17.0% of the radon tests reported to CDC for New Castle County, Delaware were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.8 pCi/L. Of 3 Delaware counties with 30 or more tests for the same period, none reported a higher share; pooled, the state comes to 16.7%.
Which counties border New Castle County?
New Castle County borders 7 counties: Cecil County, MD, Salem County, NJ, Chester County, PA, Delaware County, PA, Gloucester County, NJ, Kent County, DE and Kent County, MD.
Products
New Castle County, Products
Testing a home in New Castle County
In New Castle County, 17.0% of 10,247 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 16.7% pooled across Delaware. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in New Castle 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
EcoQube Wi-Fi continuous radon monitor
- C-NRPP 2024/25: Approved
- Plug-in
- Wi-Fi
- App only
Method: Ion chamber
First reading: Within 10 minutes
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
New Castle County, Bordering counties
Counties bordering New Castle County
Calculated by Radon411- Radon levels in Kent County, MDEPA zone 3
52.6%at or above 4 pCi/L
Median 4.4 pCi/L · 57 tests · 35.6 points above New Castle County
- Radon levels in Chester County, PAEPA zone 1
29.3%at or above 4 pCi/L
Median 2.2 pCi/L · 12,912 tests · 12.3 points above New Castle County
- Radon levels in Cecil County, MDEPA zone 2
24.9%at or above 4 pCi/L
Median 1.9 pCi/L · 1,071 tests · 7.9 points above New Castle County
- Radon levels in Delaware County, PAEPA zone 1
21.0%at or above 4 pCi/L
Median 1.9 pCi/L · 9,005 tests · 4.0 points above New Castle County
- Radon levels in Kent County, DEEPA zone 3
16.9%at or above 4 pCi/L
Median 1.6 pCi/L · 1,516 tests · 0.1 points below New Castle County
- Radon levels in Salem County, NJEPA zone 2
No CDC figure for 2008 to 2017; its page reads it against its own neighbours.
- Radon levels in Gloucester County, NJEPA zone 2
No CDC figure for 2008 to 2017; its page reads it against its own neighbours.
New Castle County, Cities and towns
Cities and towns in New Castle County
The Census Bureau estimates 588,026 residents in New Castle County for July 1, 2025, 17,085 more than in 2020 (+3.0%). Packed into its land, that is 1,379 people per square mile. No town dominates: Wilmington, the largest, has 73,512 residents, 12.5% of the total. Testing is reported here more often than across the state: CDC's 10,247 reported tests for 2008 to 2017 come to 17.4 for every 1,000 residents (2025 estimate), against 11.5 for Delaware.
From Wilmington to Ardencroft, CDC publishes no figure by town: each reads New Castle County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Wilmington | 73,512 | +3.7% | 12.5% |
| Newark | 30,359 | −0.8% | 5.2% |
| Middletown | 25,798 | +10.3% | 4.4% |
| Smyrnaextends beyond New Castle County | 13,340 | +2.9% | Counted whole |
| Elsmere | 6,196 | −0.4% | 1.1% |
| New Castle | 5,726 | +3.4% | 1.0% |
| Claytonextends beyond New Castle County | 4,527 | +13.4% | Counted whole |
| Townsend | 2,985 | +8.5% | 0.5% |
| Delaware City | 1,939 | +3.0% | 0.3% |
| Bellefonte | 1,313 | +2.2% | 0.2% |
| Newport | 906 | −0.3% | 0.2% |
| Arden | 442 | +2.3% | Under 0.1% |
- Odessa
- Ardentown
- Ardencroft
15 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. “(part)” marks a place that extends into another county. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond New Castle County is counted whole, so it has no share.
New Castle County, Homes
Homes in New Castle County
Fewer than six in ten of New Castle County's 235,057 homes are detached houses (53%, against 59% across Delaware); the rest are attached, in shared buildings or mobile. The homes are older than Delaware's as a whole: half were built before 1975 (1986 for Delaware), and 31% date from before 1960. 69% of occupied homes are lived in by their owner (Delaware: 72%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | New Castle County | Delaware |
|---|---|---|
| Housing units | 235,057 | 457,958 |
| Detached houses | 53% | 59% |
| In buildings of 5 or more | 19% | 14% |
| Mobile homes | 2% | 7% |
| Built before 1960 | 31% | 21% |
| Built since 2000 | 19% | 32% |
| Middle year built | 1975 | 1986 |
| Owner-occupied | 69% | 72% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.