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
Locations and reports
Radon Levels in Mercer County, New Jersey
EPA puts Mercer County in Zone 1, its highest radon zone, and most reported tests there come back low, though 10.6% of 6,370 (2022) reached 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
10.6%
0.9 pts above NJ
- Mercer
- 10.6%
- New Jersey
- 9.7%
6,370 tests, 2022
Median result
0.9pCi/L
Below action level
- Mercer
- 0.9 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2022
Tests reported
6,370
8th of 21 by tests
- Mercer
- 6,370
- 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
8 of 21
Middle half
- Mercer
- 10.6%
- Warren
- 24.6%
By share, of 21 with 30+ tests
Read a result for Mercer County
Starts at Mercer County's median, 0.9 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 0.9 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. Mercer County's median reported result, 2022.
The data
Mercer County, At a glance
Mercer County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Mercer County in
USGS geologic potential: High across 51% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Mercer County, 2022
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 15.7% |
| 2015 | 15.7% |
| 2016 | 15.8% |
| 2017 | 12.5% |
| 2018 | 12.7% |
| 2019 | 13.2% |
| 2020 | 13.6% |
| 2021 | 12.0% |
| 2022 | 10.6% |
2022: 10.6%. Across these years the share ran from 10.6% to 15.8%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 6,370 tests reported to CDC for Mercer 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).
Mercer County, Compared
Mercer County radon figures, compared
Calculated by Radon41110.6% of its 6,370 tests in 2022 were at or above 4 pCi/L. That is 0.9 points above the 9.7% pooled from 21 New Jersey counties.
Ordered from highest share down, it comes 8th of 21 New Jersey counties with 30 or more tests for the same period. Nationally, every county with a figure for the same period pools to 23.9%; Mercer County sits 13.3 points below it.
Next door, the shares run from 6.2% in Burlington County to 21.1% in Hunterdon County, with Monmouth County, Middlesex County and Burlington County below Mercer County. The reported tests do not follow EPA's Zone 1 label for Mercer County (predicted average above 4 pCi/L): 10.6% of them reached 4 pCi/L, fewer than that label suggests.
Half the tests came in under 0.9 pCi/L and half over it; the single highest reached 265.8 pCi/L. The rest split 72.7% under 2 pCi/L and 16.7% from 2 to 4 (New Jersey: 74.9% and 15.4%). Year by year, 2014 opened at 15.7% and 2022 closed at 10.6% (down 5.1 points), with 2016 the high at 15.8%.
The busiest year on file was 2017, with 7,001 tests reported; the quietest, 2014, had 4,830.
Mercer CountyNew Jersey, pooled
| Year | Tests | Mercer County, at or above 4 pCi/L | New Jersey, pooled |
|---|---|---|---|
| 2014 | 4,830 | 15.7% | 12.8% |
| 2015 | 5,157 | 15.7% | 12.5% |
| 2016 | 5,511 | 15.8% | 12.5% |
| 2017 | 7,001 | 12.5% | 11.9% |
| 2018 | 5,444 | 12.7% | 11.0% |
| 2019 | 5,754 | 13.2% | 11.2% |
| 2020 | 6,046 | 13.6% | 11.7% |
| 2021 | 6,375 | 12.0% | 10.3% |
| 2022 | 6,370 | 10.6% | 9.7% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Mercer County, Geology
The ground under Mercer County
PredictedUSGS's geologic map splits Mercer County: 50.5% of its land is high radon potential and 49.5% moderate. The map puts 50.4% of Mercer County in the area it calls Southern Piedmont and 49.4% in Inner Coastal Plain. 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 |
|---|---|---|---|---|
| Southern Piedmont | Black shale, sandstone and siltstone. | High | 14 | 50.4% |
| Inner Coastal Plain | Cretaceous-Lower Tertiary gravel, sand, silt, clay. | Moderate | 10 | 49.4% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Mercer County beside the ground around it
Mercer County has more high-potential ground than New Jersey as a whole: 50.5% of its land against 29.8%. Of the 6 counties that border it, 3 have more high-potential ground, Hunterdon County the most at 100%.
The map rates the ground, not the air in any home.
Local help
Mercer County, Local resources
Radon testing and mitigation in Mercer County
Listed radon businesses with an address in Mercer 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.
Listed radon professionals by town: Trenton
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
Mercer County, Questions
Questions about radon in Mercer County
Are radon levels high in Mercer County?
In 2022, 10.6% of the radon tests reported to CDC for Mercer County, New Jersey were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.9 pCi/L. Of 21 New Jersey counties with 30 or more tests for the same period, 7 reported a higher share; pooled, the state comes to 9.7%.
Which counties border Mercer County?
Mercer County borders 6 counties: Middlesex County, NJ, Somerset County, NJ, Bucks County, PA, Hunterdon County, NJ, Monmouth County, NJ and Burlington County, NJ.
Products
Mercer County, Products
Testing a home in Mercer County
In Mercer County, 10.6% of 6,370 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 Mercer 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
Monitor
Hello Radon C battery radon monitor with an e-ink screen
- C-NRPP 2024/25: Not included
- Battery
- Screen
Method: Alpha spectrometry
First reading: Within 24 hours
Short-term kitFirst Alert
RD1 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 2 to 4 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Mercer County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Mercer County
Explore
Mercer County, Bordering counties
Counties bordering Mercer County
Calculated by Radon411- Radon levels in Hunterdon County, NJEPA zone 1
21.1%at or above 4 pCi/L
Median 1.4 pCi/L · 3,748 tests · 10.5 points above Mercer County
- Radon levels in Somerset County, NJEPA zone 1
15.4%at or above 4 pCi/L
Median 1.2 pCi/L · 7,679 tests · 4.8 points above Mercer County
- Radon levels in Monmouth County, NJEPA zone 1
9.8%at or above 4 pCi/L
Median 0.7 pCi/L · 9,745 tests · 0.8 points below Mercer County
- Radon levels in Middlesex County, NJEPA zone 2
7.3%at or above 4 pCi/L
Median 0.8 pCi/L · 9,594 tests · 3.3 points below Mercer County
- Radon levels in Burlington County, NJEPA zone 2
6.2%at or above 4 pCi/L
Median 0.9 pCi/L · 5,355 tests · 4.4 points below Mercer County
- Radon levels in Bucks County, PAEPA zone 1
No CDC figure for 2022; its page reads it against its own neighbours.
Mercer County, Cities and towns
Cities and towns in Mercer County
The Census Bureau estimates 399,289 residents in Mercer County for July 1, 2025, 12,855 more than in 2020 (+3.3%). Packed into its land, that is 1,779 people per square mile. Its largest town, Trenton, has 91,506 residents, 22.9% of the total. Together its 5 incorporated places hold 33.5% of those residents; the other 66.5% live outside any of them. CDC's 6,370 reported tests for 2022 work out to 16.0 per 1,000 residents (2025 estimate), close to New Jersey's 11.4.
From Trenton to Hopewell, CDC publishes no figure by town: each reads Mercer County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Trenton | 91,506 | +1.1% | 22.9% |
| Princeton | 31,469 | +2.8% | 7.9% |
| Hightstown | 6,007 | +2.1% | 1.5% |
| Pennington | 2,889 | +4.9% | 0.7% |
| Hopewell | 1,944 | +2.4% | 0.5% |
Places in Mercer County with a city page: 1 of 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).
Mercer County, Homes
Homes in Mercer County
Fewer than six in ten of Mercer County's 150,600 homes are detached houses (47%, against 53% across New Jersey); the rest are attached, in shared buildings or mobile. Half of its homes were built before 1967, close to New Jersey's 1969: 41% date from before 1960 and 14% from 2000 or later. 62% 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 | Mercer County | New Jersey |
|---|---|---|
| Housing units | 150,600 | 3,775,842 |
| Detached houses | 47% | 53% |
| In buildings of 5 or more | 23% | 22% |
| Mobile homes | under 1% | 1% |
| Built before 1960 | 41% | 38% |
| Built since 2000 | 14% | 15% |
| Middle year built | 1967 | 1969 |
| Owner-occupied | 62% | 64% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.