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 Franklin County, Missouri
EPA puts Franklin County in Zone 2, its middle radon zone, and only 20 radon tests from it are on file with CDC (2023). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Share at 4+ pCi/L
33.2%
2.6 pts above MO
- Franklin
- 33.2%
- Missouri
- 30.6%
753 tests, 2008 to 2017
Median result
2.6pCi/L
Below action level
- Franklin
- 2.6 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
753
13th of 72 by tests
- Franklin
- 753
- St. Louis
- 17,747
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 Missouri
30 of 72
Middle half
- Franklin
- 33.2%
- Atchison
- 69.9%
By share, of 72 with 30+ tests
Read a result for Franklin County
Starts at Franklin County's median, 2.6 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.6 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. Franklin County's median reported result, 2008 to 2017.
The data
Franklin County, At a glance
Franklin County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Franklin County is a
USGS geologic potential: Moderate across 100% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Franklin County, 2023
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 30.0% |
| 2015 | 30.3% |
| 2016 | 26.0% |
| 2017 | 25.6% |
| 2018 | 57.1% |
| 2019 | 14.3% |
| 2020 | 80.0% |
| 2021 | 33.3% |
| 2022 | 42.3% |
| 2023 | 45.0% |
2023: 45.0%. Across these years the share ran from 14.3% to 80.0%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
Only 20 tests were reported to CDC for Franklin County over 2023, and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor this house.
Measured: CDC tracking data. Figure above: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).
Franklin County, Compared
Franklin County radon figures, compared
Calculated by Radon411In Franklin County, about 3 in 10 reported tests over the 2008 to 2017 laboratory totals (250 of 753) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 2.5 points lower. Across 115 Missouri counties pooled together, 30.6% of tests reached that level, so Franklin County runs 2.6 points above its state.
The newest figure, in 2023, counts only 20 tests (45.0% at or above 4 pCi/L), too few to compare, so this reading uses the 753-test figure.
Of 7 neighbours with a figure, 2 reported a larger share at or above 4 pCi/L and 5 a smaller one; the spread is 14.7% (Crawford County) to 41.6% (Jefferson County). By share, Franklin County is 30th of 72 Missouri counties with 30 or more tests for the same period.
Year by year, 2014 opened at 30.0% and 2017 closed at 25.6% (down 4.4 points), with 2015 the high at 30.3%. Half the tests came in under 2.6 pCi/L and half over it; the single highest reached 36.1 pCi/L. Below the action level, 292 tests (38.8%) came in under 2 pCi/L, against 41.2% statewide, and 211 tests (28.0%) fell between 2 and 4, against 28.1% statewide.
Zone 2 on EPA's map (predicted average between 2 and 4 pCi/L) and a 33.2% share point the same way here. USGS geology rates 100% of the county's land moderate radon potential. CDC also counts 34 tests taken after mitigation in Franklin County for the same period: tests in homes where a fix was already in.
The busiest year on file was 2016, with 50 tests reported; the quietest, 2020, had 5.
Franklin CountyMissouri, pooled
25.6% % of tests37.0% % of tests
| Year | Tests | Franklin County, at or above 4 pCi/L | Missouri, pooled |
|---|---|---|---|
| 2014 | 40 | 30.0% | 34.4% |
| 2015 | 33 | 30.3% | 27.6% |
| 2016 | 50 | 26.0% | 29.8% |
| 2017 | 39 | 25.6% | 37.0% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Franklin County, Geology
The ground under Franklin County
PredictedUSGS's geologic map puts all of Franklin County's mapped land in one class: moderate radon potential. All of it lies in the area the map calls Salem Plateau, to which USGS gives a radon index of 11, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Salem Plateau | Ordovician dolomite, sandstone, limestone, and shale. | Moderate | 11 | 100% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Franklin County beside the ground around it
Across Missouri 8.2% of the land is rated high; none of Franklin County's is. Of the 7 counties that border it, 1 has more high-potential ground, Washington County the most at 5.1%.
The map rates the ground, not the air in any home.
Local help
Franklin County, Local resources
Radon testing and mitigation in Franklin County
- Missouri Radon ProgramMissouri Radon Program, run by Missouri Department of Health and Senior Services, offers free or discounted test kits, and answers questions about testing and mitigation in Missouri.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Free radon test kits are available for Missouri residents (limit one per household).
- Compare kits
- Professionals in Missouri27 professionals are listed in Missouri.
What Missouri's program says
- Phone
- 573-751-6102
- radon@health.mo.gov
What it means
Franklin County, Questions
Questions about radon in Franklin County
Are radon levels high in Franklin County?
In 2023, 45.0% of the radon tests reported to CDC for Franklin County, Missouri were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.8 pCi/L. Of 72 Missouri counties with 30 or more tests for the same period, 29 reported a higher share; pooled, the state comes to 30.6%.
Which counties border Franklin County?
Franklin County borders 7 counties: Warren County, Gasconade County, St. Charles County, Jefferson County, St. Louis County, Crawford County and Washington County.
Products
Franklin County, Products
Testing a home in Franklin County
In Franklin County, 33.2% of 753 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 30.6% pooled across Missouri. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Franklin 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
Franklin County, Bordering counties
Counties bordering Franklin County
Calculated by Radon411- Radon levels in Jefferson CountyEPA zone 2
41.6%at or above 4 pCi/L
Median 3.1 pCi/L · 2,652 tests · 8.4 points above Franklin County
- Radon levels in Warren CountyEPA zone 2
36.8%at or above 4 pCi/L
Median 2.7 pCi/L · 285 tests · 3.6 points above Franklin County
- Radon levels in Gasconade CountyEPA zone 2
31.8%at or above 4 pCi/L
Median 2.3 pCi/L · 44 tests · 1.4 points below Franklin County
- Radon levels in St. Charles CountyEPA zone 2
26.5%at or above 4 pCi/L
Median 2.2 pCi/L · 7,001 tests · 6.7 points below Franklin County
- Radon levels in St. Louis CountyEPA zone 2
26.3%at or above 4 pCi/L
Median 2.3 pCi/L · 17,747 tests · 6.9 points below Franklin County
- Radon levels in Washington CountyEPA zone 2
26.3%at or above 4 pCi/L
Median 1.5 pCi/L · 38 tests · 6.9 points below Franklin County
- Radon levels in Crawford CountyEPA zone 2
14.7%at or above 4 pCi/L
Median 1.5 pCi/L · 34 tests · 18.5 points below Franklin County
Franklin County, Cities and towns
Cities and towns in Franklin County
The Census Bureau estimates 108,090 residents in Franklin County for July 1, 2025, 3,238 more than in 2020 (+3.1%). That works out to 117 people per square mile of land. No town dominates: Washington, the largest, has 15,906 residents, 14.7% of the total. CDC's 753 reported tests for 2008 to 2017 work out to 7.0 per 1,000 residents (2025 estimate), close to Missouri's 9.3.
From Washington to Charmwood, CDC publishes no figure by town: each reads Franklin County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Washington | 15,906 | +8.2% | 14.7% |
| Union | 13,445 | +8.6% | 12.4% |
| Pacificextends beyond Franklin County | 7,824 | +6.8% | Counted whole |
| Sullivanextends beyond Franklin County | 6,942 | +0.6% | Counted whole |
| St. Clair | 4,813 | Level | 4.5% |
| New Haven | 2,397 | −1.0% | 2.2% |
| Gerald | 1,350 | −1.5% | 1.2% |
| Parkway | 636 | −3.0% | 0.6% |
| Oak Grove Village | 407 | −2.2% | 0.4% |
| Berger | 271 | +0.7% | 0.3% |
| Leslie | 156 | +0.6% | 0.1% |
| Miramiguoa Park | 122 | Level | 0.1% |
- Charmwood
13 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. “(part)” marks a place that extends into another county. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond Franklin County is counted whole, so it has no share.
Franklin County, Homes
Homes in Franklin County
Franklin County is a place of houses on their own lots: 76% of its 45,843 homes are detached single-family houses, against 70% across Missouri. Half of its homes were built before 1984, close to Missouri's 1978: 21% date from before 1960 and 26% from 2000 or later. Owners live in 76% of the occupied homes (Missouri: 68%), so for most households a test and a fix are their own to order.
| Homes | Franklin County | Missouri |
|---|---|---|
| Housing units | 45,843 | 2,809,501 |
| Detached houses | 76% | 70% |
| In buildings of 5 or more | 6% | 13% |
| Mobile homes | 9% | 5% |
| Built before 1960 | 21% | 28% |
| Built since 2000 | 26% | 21% |
| Middle year built | 1984 | 1978 |
| Owner-occupied | 76% | 68% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.