Radon in Hillsborough County, New Hampshire
Hillsborough County, New Hampshire, is in EPA radon Zone 2: predicted average indoor radon screening level from 2 to 4 pCi/L (moderate potential). Radon laboratories reported 3,558 building tests here for 2008 to 2017: median 2.5 pCi/L, with 34.4% at or above EPA's 4 pCi/L action level (New Hampshire 34.9%, US 36.5%).
Radon test results in Hillsborough County
| Test results | Period | Tests | Typical result | 4 pCi/L or more |
|---|---|---|---|---|
| Radon testing laboratories | 2008-2017 | 3,558 | median 2.5 pCi/L | 34.4% |
| New Hampshire radon program | 2021 | 533 | median 3.2 pCi/L | 41.5% |
| New Hampshire, all counties (labs) | 2008-2017 | 10,471 | n/a | 34.9% |
| United States (labs) | 2008-2017 | 1,408,802 | n/a | 36.5% |
Test results describe buildings whose owners chose to test and whose results reached the lab or agency, not a random sample; small counts swing widely. State and US shares are computed from county counts and percents. The laboratory data comes from national radon testing laboratories and supplements EPA's zone map.
Radon in nearby counties
| County | EPA zone | Lab tests | 4 pCi/L or more |
|---|---|---|---|
| Cheshire County, NH | Zone 2 | 600 | 20.4% |
| Merrimack County, NH | Zone 2 | 884 | 31.4% |
| Rockingham County, NH | Zone 2 | 2,535 | 41.9% |
| Middlesex County, MA | Zone 1 | 30,142 | 22% |
| Sullivan County, NH | Zone 2 | 203 | 25.1% |
| Worcester County, MA | Zone 1 | 16,822 | 33.5% |
The six counties with the nearest centers.
What to do about radon in Hillsborough County
Test the building. EPA recommends fixing a home at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, and says there is no known safe level of exposure. New Hampshire's state radon program can point you to testers and test kits.
Buying here? The Environmental Records Report lists this county's radon zone and test results with the flood zone, mapped faults, power lines and federal contamination records near the address.
Radon in Hillsborough County: questions
What is the radon level in Hillsborough County?
The median of the 3,558 laboratory tests reported for Hillsborough County (2008 to 2017) was 2.5 pCi/L, and 34.4% of them were at or above 4 pCi/L. These are results of tested buildings; a single home can be far above or below them.
Is Hillsborough County in radon Zone 1?
No. EPA's 1993 map puts Hillsborough County in Zone 2 (predicted average indoor radon screening level from 2 to 4 pCi/L (moderate potential)). EPA says homes in every zone can have high radon and should be tested.
How does radon in Hillsborough County compare with New Hampshire?
34.4% of laboratory tests in Hillsborough County were at or above 4 pCi/L for 2008 to 2017, against 34.9% across New Hampshire (10,471 tests) and 36.5% nationally. 1 of New Hampshire's 10 counties are in Zone 1.
Should I test for radon in Hillsborough County?
Yes. EPA recommends testing every home whatever its zone: "This map should not be used to determine if individual homes need to be tested." Fix the home at 4 pCi/L or more and consider a fix between 2 and 4 pCi/L; EPA says there is no known safe level of radon exposure.
More for Hillsborough County
- Hillsborough loan limitsThis year's FHFA conforming, FHA and VA county loan limits for 1 to 4 unit homes, from FHFA's and HUD's official files.
- Hillsborough fair market rentHUD Fair Market Rents for studios to 4 bedrooms, the voucher payment standard range and the change from last year.
- Hillsborough property tax rateEffective property tax rate from Census survey data: median taxes paid against median home value, ranked in the state.
- Environmental records reportSuperfund, hazardous waste, leaking tank and brownfield sites near any Hillsborough address, with distances and a site map. A records search, not a Phase I.
- Superfund sites in New HampshireEvery EPA Superfund site in New Hampshire with its status, county and a map, refreshed nightly from federal records.
- USDA eligibility map: New HampshireHow much of each New Hampshire county is in a USDA-eligible rural area, the towns mapped ineligible, and a free address check.
- Opportunity zones in New HampshireEvery designated Opportunity Zone tract in New Hampshire by county, from the IRS list, and the tracts eligible for the 2027 round.
- Census tract lookupThe census tract of any Hillsborough address with its FFIEC income level and HUD Qualified Census Tract and DDA status.
Other free hazard lookups
- Fault lines near an addressUSGS-mapped earthquake faults within 5 miles, their age and slip rate, and the USGS seismic hazard value.
- Power lines near an addressHigh-voltage transmission lines within 1 mile from federal maps, with voltage and distance.
- Flood zone lookupThe FEMA flood zone mapped at any US address. Not an official flood zone determination.
- Superfund sites near an addressThe nearest EPA Superfund (NPL) sites and their status.
All of these, plus wetlands, FEMA hazard ratings and the federal contamination lists, are in the Environmental Records Report for any US address ($29).
Radon in every New Hampshire county · Radon map of every state
Data compiled 2026-10-20. County FIPS 33011. County-level screening information, not a radon measurement of any building.