Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Warren County, New Jersey
EPA puts Warren County in Zone 1, its highest radon zone, and 24.6% of its 2,819 reported radon tests (2022) 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
24.6%
14.9 pts above NJ
- Warren
- 24.6%
- New Jersey
- 9.7%
2,819 tests, 2022
Median result
1.5pCi/L
Below action level
- Warren
- 1.5 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2022
Tests reported
2,819
15th of 21 by tests
- Warren
- 2,819
- Bergen
- 11,440
Reported to CDC before any fix, 2022
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in New Jersey
1 of 21
Top quarter
- Warren
- 24.6%
- Warren
- 24.6%
By share, of 21 with 30+ tests
Read a result for Warren County
Starts at Warren County's median, 1.5 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 1.5 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. Warren County's median reported result, 2022.
The data
Warren County, At a glance
Warren County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Warren County in
USGS geologic potential: High across 95% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Warren County, 2022
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 26.7% |
| 2015 | 30.3% |
| 2016 | 31.9% |
| 2017 | 29.8% |
| 2018 | 28.1% |
| 2019 | 28.7% |
| 2020 | 28.1% |
| 2021 | 23.9% |
| 2022 | 24.6% |
2022: 24.6%. Across these years the share ran from 23.9% to 31.9%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 2,819 tests reported to CDC for Warren County over 2022, 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: 2022. Measured data period: 2014 to 2022 (every CDC figure on file).
Warren County, Compared
Warren County radon figures, compared
Calculated by Radon411Warren County's 2,819 reported tests in 2022 had a middle value of 1.5 pCi/L and a maximum of 102.5 pCi/L, and 24.6% reached 4 pCi/L. New Jersey as a whole (21 New Jersey counties, pooled) comes to 9.7%: 14.9 points lower than here.
Among its state's counties it ranks 1st of 21 New Jersey counties with 30 or more tests for the same period. Statewide for the same period, Sussex County reported the highest share (22.3%) and Cape May County the lowest (0.0%).
Below the action level, 1,607 tests (57.0%) came in under 2 pCi/L, against 74.9% statewide, and 518 tests (18.4%) fell between 2 and 4, against 15.4% statewide. The busiest year on file was 2021, with 3,645 tests reported; the quietest, 2015, had 2,213.
EPA's 1993 zone map puts Warren County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 95% of the county's land high radon potential.
Next door, the shares run from 13.6% in Morris County to 22.3% in Sussex County, with Sussex County, Hunterdon County and Morris County below Warren County. Over 9 years of annual figures the share fell 2.1 points, from 26.7% in 2014 to 24.6% in 2022; its peak was 31.9% in 2016.
Warren CountyNew Jersey, pooled
24.6% % of tests9.7% % of tests
| Year | Tests | Warren County, at or above 4 pCi/L | New Jersey, pooled |
|---|---|---|---|
| 2014 | 2,318 | 26.7% | 12.8% |
| 2015 | 2,213 | 30.3% | 12.5% |
| 2016 | 2,474 | 31.9% | 12.5% |
| 2017 | 2,679 | 29.8% | 11.9% |
| 2018 | 2,672 | 28.1% | 11.0% |
| 2019 | 2,879 | 28.7% | 11.2% |
| 2020 | 3,473 | 28.1% | 11.7% |
| 2021 | 3,645 | 23.9% | 10.3% |
| 2022 | 2,819 | 24.6% | 9.7% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Warren County, Geology
The ground under Warren County
PredictedMost of the ground under Warren County is one class on USGS's geologic map: 95.4% of its land is high radon potential, with 4.6% moderate. The map puts 57.9% of Warren County in the area it calls Highlands and 36.8% in Valley and Ridge, with 2 smaller areas beside them. USGS gives the first a radon index of 15 and the second 14, both in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Highlands | Glacial deposits, granite, pegmatites, and gneiss. | High | 15 | 57.9% |
| Valley and Ridge | Cambrian and Ordovician limestone, sandstone, siltstone, shale. | High | 14 | 36.8% |
| Valley and Ridge | Silurian and Devonian conglomerate, sandstone, shale, and limestone. | Moderate | 11 | 4.6% |
| Great Valley Section | Sandstone, shale and siltstone. | High | 15 | 0.6% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Warren County beside the ground around it
Warren County has more high-potential ground than New Jersey as a whole: 95.4% of its land against 29.8%. Of the 6 counties that border it, 2 have more high-potential ground, Hunterdon County the most at 100%.
The map rates the ground, not the air in any home.
Local help
Warren County, Local resources
Radon testing and mitigation in Warren County
- Radon SectionRadon Section, run by New Jersey Department of Environmental Protection, licenses or certifies radon professionals, offers free or discounted test kits and states the rule for disclosing radon when a home is sold, and answers questions about testing and mitigation in New Jersey.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Check with your municipal or county health department for free radon test kits or purchase a test kit from a hardware store or a NJ certified radon business.
- Compare kits
- Professionals in New Jersey15 professionals are listed in New Jersey.
What New Jersey's program says
- Phone
- 800-648-0394
- Licensing of radon professionals
By law, all businesses and professionals conducting radon testing and mitigation in New Jersey must be certified by the DEP.
- Disclosure when a home is sold or rented
Under the law, the seller must provide the buyer, at the time the contract of sale is entered into, with a copy of the results of the radon test and evidence of any mitigation or treatment.
What it means
Warren County, Questions
Questions about radon in Warren County
Are radon levels high in Warren County?
In 2022, 24.6% of the radon tests reported to CDC for Warren County, New Jersey were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.5 pCi/L. Of 21 New Jersey counties with 30 or more tests for the same period, none reported a higher share; pooled, the state comes to 9.7%.
Which counties border Warren County?
Warren County borders 6 counties: Morris County, NJ, Hunterdon County, NJ, Sussex County, NJ, Monroe County, PA, Northampton County, PA and Bucks County, PA.
Products
Warren County, Products
Testing a home in Warren County
In Warren County, 24.6% of 2,819 tests reported to CDC in 2022 reached 4 pCi/L, against 9.7% pooled across New Jersey. In Zone 1 the year-round level in Warren County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.
Test kits and monitors3
See every kit and monitor
MonitorX-Sense
XR0A-iR Wi-Fi battery radon detector with a screen
- C-NRPP 2024/25: Not included
- Battery
- Wi-Fi
- Screen, app
Method: Alpha spectrometry
First reading: Within 24 hours
Short-term kitKidde
442020 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 3 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Warren County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Warren County
Explore
Warren County, Bordering counties
Counties bordering Warren County
Calculated by Radon411- Radon levels in Sussex County, NJEPA zone 1
22.3%at or above 4 pCi/L
Median 1.5 pCi/L · 4,116 tests · 2.3 points below Warren County
- Radon levels in Hunterdon County, NJEPA zone 1
21.1%at or above 4 pCi/L
Median 1.4 pCi/L · 3,748 tests · 3.5 points below Warren County
- Radon levels in Morris County, NJEPA zone 1
13.6%at or above 4 pCi/L
Median 1.1 pCi/L · 10,939 tests · 11.0 points below Warren County
- Radon levels in Monroe County, PAEPA zone 1
No CDC figure for 2022; its page reads it against its own neighbours.
- Radon levels in Northampton County, PAEPA zone 1
No CDC figure for 2022; its page reads it against its own neighbours.
- Radon levels in Bucks County, PAEPA zone 1
No CDC figure for 2022; its page reads it against its own neighbours.
Warren County, Cities and towns
Cities and towns in Warren County
The Census Bureau estimates 112,953 residents in Warren County for July 1, 2025, 3,522 more than in 2020 (+3.2%). That works out to 317 people per square mile of land. No town dominates: Phillipsburg, the largest, has 15,456 residents, 13.7% of the total. Together its 5 incorporated places hold 33.5% of those residents; the other 66.5% live outside any of them. Testing is reported here more often than across the state: CDC's 2,819 reported tests for 2022 come to 25.0 for every 1,000 residents (2025 estimate), against 11.4 for New Jersey.
From Phillipsburg to Alpha, CDC publishes no figure by town: each reads Warren County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Phillipsburg | 15,456 | +1.7% | 13.7% |
| Hackettstown | 10,185 | −0.4% | 9.0% |
| Washington | 7,326 | +1.3% | 6.5% |
| Belvidere | 2,551 | +1.4% | 2.3% |
| Alpha | 2,362 | +1.6% | 2.1% |
5 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).
Warren County, Homes
Homes in Warren County
Of Warren County's 46,675 homes, 68% are detached houses, against 53% across New Jersey; 12% are in buildings of five or more homes. Half of its homes were built before 1972, close to New Jersey's 1969: 37% date from before 1960 and 15% from 2000 or later. 74% of occupied homes are lived in by their owner (New Jersey: 64%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Warren County | New Jersey |
|---|---|---|
| Housing units | 46,675 | 3,775,842 |
| Detached houses | 68% | 53% |
| In buildings of 5 or more | 12% | 22% |
| Mobile homes | 1% | 1% |
| Built before 1960 | 37% | 38% |
| Built since 2000 | 15% | 15% |
| Middle year built | 1972 | 1969 |
| Owner-occupied | 74% | 64% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.