Short-term kit
Radon Short Term Test Kit short-term charcoal radon test kit, lab fee included
- Lab fee included
Method: Charcoal
In home: 2 to 7 days
Locations and reports
Radon Levels in Knox County, Maine
EPA puts Knox County in Zone 2, its middle radon zone, and 29.6% of its 287 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
29.6%
8.0 pts below ME
- Knox
- 29.6%
- Maine
- 37.6%
287 tests, 2008 to 2017
Median result
2.3pCi/L
Below action level
- Knox
- 2.3 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
287
9th of 16 by tests
- Knox
- 287
- Cumberland
- 4,076
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 Maine
13 of 16
Lowest quarter
- Knox
- 29.6%
- York
- 48.4%
By share, of 16 with 30+ tests
Read a result for Knox County
Starts at Knox County's median, 2.3 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.3 pCi/L
Between 2 and 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is between 2 and 4 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Knox County's median reported result, 2008 to 2017.
The data
Knox County, At a glance
Knox County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Knox County is a
USGS geologic potential: High across 60% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Knox County, 2008 to 2017, laboratory
Under 2 pCi/L: 45%2 to 4 pCi/L: 25%4 pCi/L and above: 30%
Of 287 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 130 | 45.3% |
| 2 to 4 pCi/L | 72 | 25.1% |
| 4 pCi/L and above | 85 | 29.6% |
What these figures count
These are the 287 tests reported to CDC for Knox 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).
Knox County, Compared
Knox County radon figures, compared
Calculated by Radon411Knox County's 287 reported tests over the 2008 to 2017 laboratory totals had a middle value of 2.3 pCi/L and a maximum of 38.9 pCi/L, and 29.6% reached 4 pCi/L. Maine as a whole (16 Maine counties, pooled) comes to 37.6%: 8.0 points higher than here.
Among its state's counties it ranks 13th of 16 Maine counties with 30 or more tests for the same period. Statewide for the same period, York County reported the highest share (48.4%) and Penobscot County the lowest (16.4%).
Below the action level, 130 tests (45.3%) came in under 2 pCi/L, against 41.4% statewide, and 72 tests (25.1%) fell between 2 and 4, against 21.0% statewide. CDC's ten-year totals for Knox County went from 227 tests (2005 to 2014) to 287 (2008 to 2017), the share going from 28.6% to 29.6%.
EPA's 1993 zone map puts Knox County in Zone 2, a predicted county average between 2 and 4 pCi/L. USGS geology rates 60% of the county's land high radon potential.
Next door, the shares run from 32.1% in Waldo County to 39.1% in Hancock County.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Knox County, Geology
The ground under Knox County
PredictedUSGS's geologic map splits Knox County: 60.1% of its land is high radon potential and 18.6% moderate and 9.2% low. The map puts 52.6% of Knox County in the area it calls Coastal Province and 18.6% in Moose River Lowlands/Central Maine Lowlands/Central Maine Highlands/Coastal Province, with 2 smaller areas beside them. USGS gives the first a radon index of 13, in the high band (12 to 17), and the second 11, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Coastal Province | Granite, granodiorite, and mafic metamorphic rocks. | High | 13 | 52.6% |
| Moose River Lowlands/Central Maine Lowlands/Central Maine Highlands/Coastal Province | Heterogeneous metamorphic and igneous rocks. | Moderate | 11 | 18.6% |
| Coastal Province | Glacial lake clay and marine clay. | Low | 8 | 9.2% |
| Coastal Province | Granites and lesser amounts of metamorphic rocks. | High | 13 | 7.5% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Knox County beside the ground around it
Knox County has more high-potential ground than Maine as a whole: 60.1% of its land against 24.5%. Of the 3 counties that border it, none has as large a share of high-potential ground; Hancock County comes nearest at 43.4%.
The map rates the ground, not the air in any home.
Local help
Knox County, Local resources
Radon testing and mitigation in Knox County
- Maine Radiation Control ProgramMaine Radiation Control Program, run by Maine Center for Disease Control & Prevention, licenses or certifies radon professionals, and answers questions about testing and mitigation in Maine.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
- See the Maine directoryNo professionals are listed in Maine yet. The state program can point you to registered testers and mitigators.
What Maine's program says
- Phone
- 207-287-5676
- radon.dhhs@maine.gov
- Licensing of radon professionals
Under Maine law, only the owner or occupant of a residence or someone registered with the state to provide these services, may test for radon, install and/or advise on the installation of a radon reduction (mitigation) system.
What it means
Knox County, Questions
Questions about radon in Knox County
Are radon levels high in Knox County?
Over the 2008 to 2017 laboratory totals, 29.6% of the radon tests reported to CDC for Knox County, Maine were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.3 pCi/L. Of 16 Maine counties with 30 or more tests for the same period, 12 reported a higher share; pooled, the state comes to 37.6%.
Which counties border Knox County?
Knox County borders 3 counties: Lincoln County, Waldo County and Hancock County.
Products
Knox County, Products
Testing a home in Knox County
In Knox County, 29.6% of 287 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 37.6% pooled across Maine. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Knox County; a long-term test tells the year-round average.
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
MonitorX-Sense
XR0B-SR battery digital radon monitor with an alarm
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Alpha spectrometry
First reading: Within 24 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Knox County, Bordering counties
Counties bordering Knox County
Calculated by Radon411- Radon levels in Hancock CountyEPA zone 1
39.1%at or above 4 pCi/L
Median 2.6 pCi/L · 327 tests · 9.5 points above Knox County
- Radon levels in Lincoln CountyEPA zone 1
35.8%at or above 4 pCi/L
Median 2.5 pCi/L · 246 tests · 6.2 points above Knox County
- Radon levels in Waldo CountyEPA zone 2
32.1%at or above 4 pCi/L
Median 2.3 pCi/L · 209 tests · 2.5 points above Knox County
Knox County, Cities and towns
Cities and towns in Knox County
The Census Bureau estimates 41,117 residents in Knox County for July 1, 2025, 454 more than in 2020 (+1.1%). That works out to 113 people per square mile of land. Rockland, its one incorporated place, has 7,142 residents, 17.4% of the total. CDC's 287 reported tests for 2008 to 2017 work out to 7.0 per 1,000 residents (2025 estimate), close to Maine's 8.4.
Rockland is the one incorporated place here; CDC publishes no figure by town, so it reads Knox County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Rockland | 7,142 | +2.7% | 17.4% |
One incorporated place, 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).
Knox County, Homes
Homes in Knox County
Knox County is a place of houses on their own lots: 79% of its 24,428 homes are detached single-family houses, against 70% across Maine. Half of its homes were built before 1973, close to Maine's 1976: 41% date from before 1960 and 17% from 2000 or later. Owners live in 79% of the occupied homes (Maine: 74%), so for most households a test and a fix are their own to order.
| Homes | Knox County | Maine |
|---|---|---|
| Housing units | 24,428 | 746,552 |
| Detached houses | 79% | 70% |
| In buildings of 5 or more | 5% | 9% |
| Mobile homes | 6% | 8% |
| Built before 1960 | 41% | 35% |
| Built since 2000 | 17% | 20% |
| Middle year built | 1973 | 1976 |
| Owner-occupied | 79% | 74% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.