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 Boise County, Idaho
EPA puts Boise County in Zone 1, its highest radon zone, and 22.4% of its 58 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
22.4%
19.1 pts below ID
- Boise
- 22.4%
- Idaho
- 41.5%
58 tests, 2008 to 2017
Median result
2.0pCi/L
Below action level
- Boise
- 2.0 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
58
29th of 37 by tests
- Boise
- 58
- Ada
- 3,030
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in Idaho
29 of 37
Lowest quarter
- Boise
- 22.4%
- Bear Lake
- 78.1%
By share, of 37 with 30+ tests
Read a result for Boise County
Starts at Boise County's median, 2.0 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.0 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. Boise County's median reported result, 2008 to 2017.
The data
Boise County, At a glance
Boise County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Boise County in
USGS geologic potential: High across 100% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Boise County, 2008 to 2017, laboratory
Under 2 pCi/L: 48%2 to 4 pCi/L: 29%4 pCi/L and above: 23%
Of 58 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 28 | 48.3% |
| 2 to 4 pCi/L | 17 | 29.3% |
| 4 pCi/L and above | 13 | 22.4% |
What these figures count
These are the 58 tests reported to CDC for Boise 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).
Boise County, Compared
Boise County radon figures, compared
Calculated by Radon411Boise County's 58 reported tests over the 2008 to 2017 laboratory totals had a middle value of 2.0 pCi/L and a maximum of 32.8 pCi/L, and 22.4% reached 4 pCi/L. Idaho as a whole (44 Idaho counties, pooled) comes to 41.5%: 19.1 points higher than here.
Among its state's counties it ranks 29th of 37 Idaho counties with 30 or more tests for the same period. Statewide for the same period, Bear Lake County reported the highest share (78.1%) and Payette County the lowest (4.9%).
Below the action level, 28 tests (48.3%) came in under 2 pCi/L, against 31.5% statewide, and 17 tests (29.3%) fell between 2 and 4, against 26.9% statewide. CDC's ten-year totals for Boise County went from 52 tests (2005 to 2014) to 58 (2008 to 2017), the share going from 26.9% to 22.4%.
EPA's 1993 zone map puts Boise County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 100% of the county's land high radon potential.
Next door, the shares run from 20.2% in Gem County to 72.7% in Custer County, with Gem County below Boise County.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Boise County, Geology
The ground under Boise County
PredictedMost of the ground under Boise County is one class on USGS's geologic map: 99.9% of its land is high radon potential, with 0.1% low. All of it lies in the area the map calls Northern Rocky Mountain Province, to which USGS gives a radon index of 12, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Northern Rocky Mountain Province | Diorite and granite of the Idaho batholith. | High | 12 | 99.9% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Boise County beside the ground around it
Boise County has more high-potential ground than Idaho as a whole: 99.9% of its land against 50.7%. Of the 5 counties that border it, 1 has more high-potential ground, Custer County the most at 100%.
The map rates the ground, not the air in any home.
Local help
Boise County, Local resources
Radon testing and mitigation in Boise County
- DHW Environmental Health ProgramDHW Environmental Health Program, run by Idaho Department of Health and Welfare, offers free or discounted test kits, and answers questions about testing and mitigation in Idaho.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Order a free radon test kit.
- Compare kits
- See the Idaho directoryNo professionals are listed in Idaho yet. The state program can point you to registered testers and mitigators.
What Idaho's program says
- Phone
- 800-445-8647
- radon@dhw.idaho.gov
What it means
Boise County, Questions
Questions about radon in Boise County
Are radon levels high in Boise County?
Over the 2008 to 2017 laboratory totals, 22.4% of the radon tests reported to CDC for Boise County, Idaho were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.0 pCi/L. Of 37 Idaho counties with 30 or more tests for the same period, 28 reported a higher share; pooled, the state comes to 41.5%.
Which counties border Boise County?
Boise County borders 5 counties: Gem County, Ada County, Elmore County, Valley County and Custer County.
Products
Boise County, Products
Testing a home in Boise County
In Boise County, 22.4% of 58 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 41.5% pooled across Idaho. In Zone 1 the year-round level in Boise 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
Boise County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Boise County
Explore
Boise County, Bordering counties
Counties bordering Boise County
Calculated by Radon411- Radon levels in Custer CountyEPA zone 1
72.7%at or above 4 pCi/L
Median 6.8 pCi/L · 33 tests · 50.3 points above Boise County
- Radon levels in Elmore CountyEPA zone 1
48.1%at or above 4 pCi/L
Median 3.8 pCi/L · 158 tests · 25.7 points above Boise County
- Radon levels in Valley CountyEPA zone 1
27.3%at or above 4 pCi/L
Median 2.3 pCi/L · 128 tests · 4.9 points above Boise County
- Radon levels in Ada CountyEPA zone 2
25.2%at or above 4 pCi/L
Median 2.4 pCi/L · 3,030 tests · 2.8 points above Boise County
- Radon levels in Gem CountyEPA zone 3
20.2%at or above 4 pCi/L
Median 1.9 pCi/L · 99 tests · 2.2 points below Boise County
Boise County, Cities and towns
Cities and towns in Boise County
Boise County is growing: the Census Bureau puts it at 8,545 residents on July 1, 2025, up 11.5% from 7,662 in 2020. Spread over its land, that is 4.5 people to the square mile. No town dominates: Horseshoe Bend, the largest, has 816 residents, 9.5% of the total. Together its 4 incorporated places hold 18.4% of those residents; the other 81.6% live outside any of them. CDC's 58 reported tests for 2008 to 2017 work out to 6.8 per 1,000 residents (2025 estimate), close to Idaho's 6.4.
From Horseshoe Bend to Placerville, CDC publishes no figure by town: each reads Boise County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Horseshoe Bend | 816 | +12.7% | 9.5% |
| Idaho City | 531 | +12.5% | 6.2% |
| Crouch | 181 | +13.1% | 2.1% |
| Placerville | 48 | +2.1% | 0.6% |
4 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).
Boise County, Homes
Homes in Boise County
Boise County is a place of houses on their own lots: 84% of its 5,592 homes are detached single-family houses, against 74% across Idaho. Half of its homes were built before 1991, close to Idaho's 1990: 9% date from before 1960 and 28% from 2000 or later. Owners live in 88% of the occupied homes (Idaho: 72%), so for most households a test and a fix are their own to order.
| Homes | Boise County | Idaho |
|---|---|---|
| Housing units | 5,592 | 776,683 |
| Detached houses | 84% | 74% |
| In buildings of 5 or more | under 1% | 9% |
| Mobile homes | 14% | 7% |
| Built before 1960 | 9% | 18% |
| Built since 2000 | 28% | 35% |
| Middle year built | 1991 | 1990 |
| Owner-occupied | 88% | 72% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.