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 Ventura County, California
EPA puts Ventura County in Zone 1, its highest radon zone, and most reported tests there come back low, though 11.9% of 335 (2008 to 2017, laboratory totals) 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
11.9%
1.6 pts above CA
- Ventura
- 11.9%
- California
- 10.3%
335 tests, 2008 to 2017
Median result
1.0pCi/L
Below action level
- Ventura
- 1.0 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
335
8th of 33 by tests
- Ventura
- 335
- Los Angeles
- 2,363
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 California
14 of 33
Middle half
- Ventura
- 11.9%
- El Dorado
- 30.3%
By share, of 33 with 30+ tests
Read a result for Ventura County
Starts at Ventura County's median, 1.0 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 1.0 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. Ventura County's median reported result, 2008 to 2017.
The data
Ventura County, At a glance
Ventura County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Ventura County in
USGS geologic potential: Moderate across 98% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Ventura County, 2008 to 2017, laboratory
Under 2 pCi/L: 74%2 to 4 pCi/L: 14%4 pCi/L and above: 12%
Of 335 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 247 | 73.7% |
| 2 to 4 pCi/L | 48 | 14.3% |
| 4 pCi/L and above | 40 | 11.9% |
What these figures count
These are the 335 tests reported to CDC for Ventura 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).
Ventura County, Compared
Ventura County radon figures, compared
Calculated by Radon41111.9% of its 335 tests over the 2008 to 2017 laboratory totals were at or above 4 pCi/L. That is 1.6 points above the 10.3% pooled from 56 California counties.
Ordered from highest share down, it comes 14th of 33 California counties with 30 or more tests for the same period. Nationally, every county with a figure for the same period pools to 35.7%; Ventura County sits 23.8 points below it.
Next door, the shares run from 9.5% in Los Angeles County to 17.6% in Santa Barbara County, with Kern County and Los Angeles County below Ventura County. The reported tests do not follow EPA's Zone 1 label for Ventura County (predicted average above 4 pCi/L): 11.9% of them reached 4 pCi/L, fewer than that label suggests.
Half the tests came in under 1.0 pCi/L and half over it; the single highest reached 25.2 pCi/L. The rest split 73.7% under 2 pCi/L and 14.3% from 2 to 4 (California: 76.8% and 12.9%).
CDC's ten-year totals for Ventura County went from 331 tests (2005 to 2014) to 335 (2008 to 2017), the share going from 10.0% to 11.9%.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Ventura County, Geology
The ground under Ventura County
PredictedMost of the ground under Ventura County is one class on USGS's geologic map: 97.8% of its land is moderate radon potential, with 2.0% low. The map puts 60.8% of Ventura County in the area it calls Transverse Ranges and 37.0% in Southern Coast Ranges, with 2 smaller areas beside them. USGS gives both a radon index of 9, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Transverse Ranges | Precambrian metamorphic rocks and Mesozoic granitic rocks, and the western part is underlain by Cretaceous to Pliocene marine sedimentary rocks. | Moderate | 9 | 60.8% |
| Southern Coast Ranges | Metamorphosed marine sedimentary rocks, ultramafic rocks, Triasic metamorphic rocks, Mesozoic granitic rocks, and a series of fault-bounded linear basins in which Teriary marine and continental sedimentary rocks were deposited. | Moderate | 9 | 37.0% |
| Channel Islands | Tertiary marine sedimentary, volcanic, igneous, and metamorphic rocks. | Low | 7 | 1.2% |
| Mojave Desert | Precambrian and Paleozoic metamorphosed and unmetamorphosed sedimentary rocks, Mesozoic and Tertiary intrusive rocks, Tertiary sedimentary and volcanic rocks, and significant eolian deposits. | Low | 8 | 0.8% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Ventura County beside the ground around it
Across California 0.1% of the land is rated high; none of Ventura County's is. Of the 3 counties that border it, none has as large a share of moderate-potential ground; Santa Barbara County comes nearest at 92.7%.
The map rates the ground, not the air in any home.
Local help
Ventura County, Local resources
Radon testing and mitigation in Ventura County
- California Indoor Radon ProgramCalifornia Indoor Radon Program, run by California Department of Public Health, licenses or certifies radon professionals and offers free or discounted test kits, and answers questions about testing and mitigation in California.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Discounted test kits can be purchased through our partner laboratory, Alpha Energy, for $14.95.
- Compare kits
- Professionals in California4 professionals are listed in California.
What California's program says
- Phone
- 1-800-745-7236
- Radonprogram@cdph.ca.gov
- Licensing of radon professionals
The Radon Program certifies all radon service providers operating in California.
What it means
Ventura County, Questions
Questions about radon in Ventura County
Are radon levels high in Ventura County?
Over the 2008 to 2017 laboratory totals, 11.9% of the radon tests reported to CDC for Ventura County, California were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.0 pCi/L. Of 33 California counties with 30 or more tests for the same period, 13 reported a higher share; pooled, the state comes to 10.3%.
Which counties border Ventura County?
Ventura County borders 3 counties: Kern County, Santa Barbara County and Los Angeles County.
Products
Ventura County, Products
Testing a home in Ventura County
In Ventura County, 11.9% of 335 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 10.3% pooled across California. In Zone 1 the year-round level in Ventura 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
MonitorAEGTEST
HOUND-3699 radon monitor with a 2.1-inch touchscreen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
First reading: Within 1 hour
Short-term kitempowerDX
Standard Radon Test short-term mail-in radon test kit
- Lab fee included
Method: Passive sampler
In home: 48 to 96 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Ventura County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Ventura County
Explore
Ventura County, Bordering counties
Counties bordering Ventura County
Calculated by Radon411- Radon levels in Santa Barbara CountyEPA zone 1
17.6%at or above 4 pCi/L
Median 1.2 pCi/L · 421 tests · 5.7 points above Ventura County
- Radon levels in Kern CountyEPA zone 2
11.6%at or above 4 pCi/L
Median 1.8 pCi/L · 121 tests · 0.3 points below Ventura County
- Radon levels in Los Angeles CountyEPA zone 2
9.5%at or above 4 pCi/L
Median 0.7 pCi/L · 2,363 tests · 2.4 points below Ventura County
Ventura County, Cities and towns
Cities and towns in Ventura County
About 830,851 people live in Ventura County by the Census Bureau's estimate for July 1, 2025, 12,942 fewer than in 2020 (−1.5%). That works out to 451 people per square mile of land. Its largest town, Oxnard, has 199,651 residents, 24.0% of the total. Together its 10 incorporated places hold 88.8% of those residents; the other 11.2% live outside any of them. Testing is reported here more often than across the state: CDC's 335 reported tests for 2008 to 2017 come to 0.4 for every 1,000 residents (2025 estimate), against 0.2 for California.
From Oxnard to Ojai, CDC publishes no figure by town: each reads Ventura County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Oxnard | 199,651 | −1.1% | 24.0% |
| Simi Valley | 124,861 | −1.2% | 15.0% |
| Thousand Oaks | 122,230 | −3.6% | 14.7% |
| San Buenaventura (Ventura) | 109,914 | −0.6% | 13.2% |
| Camarillo | 68,652 | −2.9% | 8.3% |
| Moorpark | 35,023 | −3.4% | 4.2% |
| Santa Paula | 31,774 | +3.2% | 3.8% |
| Port Hueneme | 20,987 | −4.3% | 2.5% |
| Fillmore | 16,937 | +2.6% | 2.0% |
| Ojai | 7,474 | −2.0% | 0.9% |
10 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).
Ventura County, Homes
Homes in Ventura County
Of Ventura County's 294,651 homes, 63% are detached houses, against 57% across California; 16% are in buildings of five or more homes. Half of its homes were built before 1977, close to California's 1976: 15% date from before 1960 and 16% from 2000 or later. 64% of occupied homes are lived in by their owner (California: 56%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Ventura County | California |
|---|---|---|
| Housing units | 294,651 | 14,532,683 |
| Detached houses | 63% | 57% |
| In buildings of 5 or more | 16% | 24% |
| Mobile homes | 4% | 4% |
| Built before 1960 | 15% | 27% |
| Built since 2000 | 16% | 18% |
| Middle year built | 1977 | 1976 |
| Owner-occupied | 64% | 56% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.