Short-term kitKidde
442020 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 3 days
Locations and reports
Radon Levels in Ada County, Idaho
EPA puts Ada County in Zone 2, its middle radon zone, and 25.2% of its 3,030 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
25.2%
16.3 pts below ID
- Ada
- 25.2%
- Idaho
- 41.5%
3,030 tests, 2008 to 2017
Median result
2.4pCi/L
Below action level
- Ada
- 2.4 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
3,030
Most tested in Idaho
- Ada
- 3,030
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 Idaho
26 of 37
Middle half
- Ada
- 25.2%
- Bear Lake
- 78.1%
By share, of 37 with 30+ tests
Read a result for Ada County
Starts at Ada County's median, 2.4 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.4 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. Ada County's median reported result, 2008 to 2017.
The data
Ada County, At a glance
Ada County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Ada County is a
USGS geologic potential: Moderate across 89% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Ada County, 2008 to 2017, laboratory
Under 2 pCi/L: 40%2 to 4 pCi/L: 35%4 pCi/L and above: 25%
Of 3,030 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 1,193 | 39.4% |
| 2 to 4 pCi/L | 1,074 | 35.4% |
| 4 pCi/L and above | 763 | 25.2% |
What these figures count
These are the 3,030 tests reported to CDC for Ada 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).
Ada County, Compared
Ada County radon figures, compared
Calculated by Radon411Ada County's 3,030 reported tests over the 2008 to 2017 laboratory totals had a middle value of 2.4 pCi/L and a maximum of 67.3 pCi/L, and 25.2% reached 4 pCi/L. Idaho as a whole (44 Idaho counties, pooled) comes to 41.5%: 16.3 points higher than here.
Among its state's counties it ranks 26th 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, 1,193 tests (39.4%) came in under 2 pCi/L, against 31.5% statewide, and 1,074 tests (35.4%) fell between 2 and 4, against 26.9% statewide. CDC's ten-year totals for Ada County went from 1,968 tests (2005 to 2014) to 3,030 (2008 to 2017), the share going from 25.0% to 25.2%.
EPA's 1993 zone map puts Ada County in Zone 2, a predicted county average between 2 and 4 pCi/L. USGS geology rates 89% of the county's land moderate radon potential.
Next door, the shares run from 10.7% in Canyon County to 48.1% in Elmore County, with Owyhee County, Boise County and Gem County below Ada County.
CDC also counts 62 tests taken after mitigation in Ada County for the same period: tests in homes where a fix was already in.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Ada County, Geology
The ground under Ada County
PredictedMost of the ground under Ada County is one class on USGS's geologic map: 88.6% of its land is moderate radon potential, with 11.4% high. The map puts 88.6% of Ada County in the area it calls Eastern Snake river plain and Malheur-Boise-King Section and 11.4% in Northern Rocky Mountain Province. USGS gives the first a radon index of 10, in the moderate band (9 to 11), and the second 12, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Eastern Snake river plain and Malheur-Boise-King Section | Basalt flows. | Moderate | 10 | 88.6% |
| Northern Rocky Mountain Province | Diorite and granite of the Idaho batholith. | High | 12 | 11.4% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Ada County beside the ground around it
Idaho as a whole has more high-potential ground than Ada County: 50.7% of its land, against 11.4% here. Of the 5 counties that border it, 3 have more high-potential ground, Boise County the most at 99.9%.
The map rates the ground, not the air in any home.
Local help
Ada County, Local resources
Radon testing and mitigation in Ada 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
Ada County, Questions
Questions about radon in Ada County
Are radon levels high in Ada County?
Over the 2008 to 2017 laboratory totals, 25.2% of the radon tests reported to CDC for Ada County, Idaho were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.4 pCi/L. Of 37 Idaho counties with 30 or more tests for the same period, 25 reported a higher share; pooled, the state comes to 41.5%.
Which counties border Ada County?
Ada County borders 5 counties: Canyon County, Elmore County, Boise County, Gem County and Owyhee County.
Products
Ada County, Products
Testing a home in Ada County
In Ada County, 25.2% of 3,030 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 41.5% pooled across Idaho. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Ada County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
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
MonitorSafetySiren
Pro4 plug-in radon detector with a display and alarm
- C-NRPP 2024/25: Not included
- Plug-in
- Alarm
- Screen
First reading: Within 48 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Ada County, Bordering counties
Counties bordering Ada County
Calculated by Radon411- Radon levels in Elmore CountyEPA zone 1
48.1%at or above 4 pCi/L
Median 3.8 pCi/L · 158 tests · 22.9 points above Ada County
- Radon levels in Owyhee CountyEPA zone 2
23.3%at or above 4 pCi/L
Median 2.1 pCi/L · 30 tests · 1.9 points below Ada County
- Radon levels in Boise CountyEPA zone 1
22.4%at or above 4 pCi/L
Median 2.0 pCi/L · 58 tests · 2.8 points below Ada County
- Radon levels in Gem CountyEPA zone 3
20.2%at or above 4 pCi/L
Median 1.9 pCi/L · 99 tests · 5.0 points below Ada County
- Radon levels in Canyon CountyEPA zone 2
10.7%at or above 4 pCi/L
Median 1.6 pCi/L · 563 tests · 14.5 points below Ada County
Ada County, Cities and towns
Cities and towns in Ada County
Ada County is growing: the Census Bureau puts it at 546,141 residents on July 1, 2025, up 9.6% from 498,263 in 2020. That works out to 519 people per square mile of land. Its largest town, Boise City, has 238,429 residents, 43.7% of the total. CDC's 3,030 reported tests for 2008 to 2017 work out to 5.5 per 1,000 residents (2025 estimate), close to Idaho's 6.4.
From Boise City to Garden City, CDC publishes no figure by town: each reads Ada County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Boise City | 238,429 | +1.0% | 43.7% |
| Meridian | 142,988 | +19.6% | 26.2% |
| Eagle | 34,658 | +9.6% | 6.3% |
| Kuna | 31,525 | +28.5% | 5.8% |
| Starextends beyond Ada County | 20,874 | +81.7% | Counted whole |
| Garden City | 13,047 | +6.1% | 2.4% |
Places in Ada County with a city page: 1 of 1
6 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). A place that extends beyond Ada County is counted whole, so it has no share.
Ada County, Homes
Homes in Ada County
Of Ada County's 205,068 homes, 75% are detached houses, against 74% across Idaho; 11% are in buildings of five or more homes. Half of its homes were built before 1996, close to Idaho's 1990: 10% date from before 1960 and 43% from 2000 or later. 71% of occupied homes are lived in by their owner (Idaho: 72%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Ada County | Idaho |
|---|---|---|
| Housing units | 205,068 | 776,683 |
| Detached houses | 75% | 74% |
| In buildings of 5 or more | 11% | 9% |
| Mobile homes | 3% | 7% |
| Built before 1960 | 10% | 18% |
| Built since 2000 | 43% | 35% |
| Middle year built | 1996 | 1990 |
| Owner-occupied | 71% | 72% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.