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
Locations and reports
Radon Levels in Monroe County, Florida
EPA puts Monroe County in Zone 3, its lowest radon zone, and only 8 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
20.0%
2.8 pts below FL
- Monroe
- 20.0%
- Florida
- 22.8%
75 tests, 2022
Median result
2.2pCi/L
Below action level
- Monroe
- 2.2 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2022
Tests reported
75
32nd of 40 by tests
- Monroe
- 75
- Miami-Dade
- 9,033
Reported to CDC before any fix, 2022
EPA radon zone
Zone 3
Lower potential
- 1
- 2
- Zone 3
1 highest, 3 lowest
EPA predicts under 2 pCi/L indoors
Rank in Florida
7 of 40
Top quarter
- Monroe
- 20.0%
- Palm Beach
- 54.7%
By share, of 40 with 30+ tests
Read a result for Monroe County
Starts at Monroe County's median, 2.2 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.2 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. Monroe County's median reported result, 2022.
The data
Monroe County, At a glance
Monroe County at a glance
Predicted: EPA radon zone
EPA Zone 3: lower predicted potential
USGS geologic potential: Low across 70% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Monroe County, 2023
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 0.0% |
| 2016 | 100.0% |
| 2017 | 20.8% |
| 2018 | 100.0% |
| 2019 | 0.0% |
| 2021 | 0.0% |
| 2022 | 20.0% |
| 2023 | 12.5% |
2023: 12.5%. Across these years the share ran from 0.0% to 100.0%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
Only 8 tests were reported to CDC for Monroe 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).
Monroe County, Compared
Monroe County radon figures, compared
Calculated by Radon411Monroe County's 75 reported tests in 2022 had a middle value of 2.2 pCi/L and a maximum of 8.6 pCi/L, and 20.0% reached 4 pCi/L. Florida as a whole (54 Florida counties, pooled) comes to 22.8%: 2.8 points higher than here.
The newest figure, in 2023, counts only 8 tests (12.5% at or above 4 pCi/L), too few to compare, so this reading uses the 75-test figure.
Among its state's counties it ranks 7th of 40 Florida counties with 30 or more tests for the same period. Statewide for the same period, Palm Beach County reported the highest share (54.7%) and Hardee County the lowest (0.0%).
Below the action level, 36 tests (48.0%) came in under 2 pCi/L, against 52.6% statewide, and 24 tests (32.0%) fell between 2 and 4, against 24.6% statewide. The busiest year on file was 2022, with 75 tests reported; the quietest, 2021, had 1.
EPA's 1993 zone map puts Monroe County in Zone 3, a predicted county average under 2 pCi/L. USGS geology rates 70% of the county's land low radon potential.
Next door, the shares run from 15.9% in Miami-Dade County to 25.0% in Collier County, with Miami-Dade County below Monroe County. Over 3 years of annual figures the share held within 2 points, from 20.8% in 2017 to 20.0% in 2022; its peak was 20.8% in 2017.
Monroe CountyFlorida, pooled
| Year | Tests | Monroe County, at or above 4 pCi/L | Florida, pooled |
|---|---|---|---|
| 2017 | 53 | 20.8% | 21.7% |
| 2019 | 47 | 0.0% | 29.6% |
| 2022 | 75 | 20.0% | 22.8% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Monroe County, Geology
The ground under Monroe County
PredictedUSGS's geologic map puts all of Monroe County's mapped land in one class: low radon potential. 70.2% of it lies in the area the map calls Gulf/Atlantic Lowland and Central Highland, to which USGS gives a radon index of 6, in the low band (5 to 8).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Gulf/Atlantic Lowland and Central Highland | sand, silt, clay, gravel | Low | 6 | 70.2% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Monroe County beside the ground around it
Across Florida 7.1% of the land is rated moderate; none of Monroe County's is. Of the 2 counties that border it, 1 has more moderate-potential ground, Miami-Dade County the most at 17.5%.
The map rates the ground, not the air in any home.
Local help
Monroe County, Local resources
Radon testing and mitigation in Monroe County
- Florida’s Radon ProgramFlorida’s Radon Program, run by Florida Department of Health, licenses or certifies radon professionals and offers free or discounted test kits, and answers questions about testing and mitigation in Florida.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Protect your family by requesting a FREE radon test kit.
- Compare kits
- Professionals in Florida77 professionals are listed in Florida.
What Florida's program says
- Phone
- 850-245-4288
- PHtoxicology@FLhealth.gov
- Licensing of radon professionals
Florida Statutes require the certification of businesses and individuals providing radon services or any other radon related activity.
What it means
Monroe County, Questions
Questions about radon in Monroe County
Are radon levels high in Monroe County?
In 2023, 12.5% of the radon tests reported to CDC for Monroe County, Florida were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.9 pCi/L. Of 40 Florida counties with 30 or more tests for the same period, 6 reported a higher share; pooled, the state comes to 22.8%.
Which counties border Monroe County?
Monroe County borders 2 counties: Miami-Dade County and Collier County.
Products
Monroe County, Products
Testing a home in Monroe County
In Monroe County, 20.0% of 75 tests reported to CDC in 2022 reached 4 pCi/L, against 22.8% pooled across Florida. Zone 3 is the lowest label, yet homes at or above 4 pCi/L occur in every zone: a short-term kit (2 to 90 days) is the quick first check in Monroe County.
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
Monitor
Corentium Home 2 battery digital radon monitor
- C-NRPP 2024/25: Not included
- Battery
- Bluetooth
- Screen, app
Method: Alpha spectrometry
Readings: Every 60 minutes
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Monroe County, Bordering counties
Counties bordering Monroe County
Calculated by Radon411- Radon levels in Collier CountyEPA zone 3
25.0%at or above 4 pCi/L
Median 2.4 pCi/L · 8,358 tests · 5.0 points above Monroe County
- Radon levels in Miami-Dade CountyEPA zone 2
15.9%at or above 4 pCi/L
Median 1.4 pCi/L · 9,033 tests · 4.1 points below Monroe County
Monroe County, Cities and towns
Cities and towns in Monroe County
About 80,406 people live in Monroe County by the Census Bureau's estimate for July 1, 2025, 2,445 fewer than in 2020 (−3.0%). That works out to 82 people per square mile of land. Its largest town, Key West, has 24,999 residents, 31.1% of the total. Together its 5 incorporated places hold 53.4% of those residents; the other 46.6% live outside any of them. Reported testing is thin here: 75 tests over 2022, or 0.9 for every 1,000 residents (2025 estimate), where Florida as a whole comes to 2.6.
From Key West to Layton, CDC publishes no figure by town: each reads Monroe County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Key West | 24,999 | −5.2% | 31.1% |
| Marathon | 10,060 | +2.0% | 12.5% |
| Islamorada, Village of Islands | 6,955 | −2.3% | 8.6% |
| Key Colony Beach | 741 | −5.8% | 0.9% |
| Layton | 209 | −2.8% | 0.3% |
5 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).
Monroe County, Homes
Homes in Monroe County
Of Monroe County's 54,418 homes, 57% are detached houses, against 55% across Florida; 17% are in buildings of five or more homes. Half of its homes were built before 1982, close to Florida's 1988: 15% date from before 1960 and 18% from 2000 or later. 63% of occupied homes are lived in by their owner (Florida: 67%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Monroe County | Florida |
|---|---|---|
| Housing units | 54,418 | 10,082,356 |
| Detached houses | 57% | 55% |
| In buildings of 5 or more | 17% | 25% |
| Mobile homes | 9% | 8% |
| Built before 1960 | 15% | 10% |
| Built since 2000 | 18% | 30% |
| Middle year built | 1982 | 1988 |
| Owner-occupied | 63% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.