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
Locations and reports
Radon Levels in Green County, Wisconsin
EPA puts Green County in Zone 1, its highest radon zone, and 33.6% of its 235 reported radon tests (2023) 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
33.6%
2.1 pts below WI
- Green
- 33.6%
- Wisconsin
- 35.7%
235 tests, 2023
Median result
2.1pCi/L
Below action level
- Green
- 2.1 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2023
Tests reported
235
25th of 69 by tests
- Green
- 235
- Dane
- 2,887
Reported to CDC before any fix, 2023
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in Wisconsin
44 of 69
Middle half
- Green
- 33.6%
- Langlade
- 65.8%
By share, of 69 with 30+ tests
Read a result for Green County
Starts at Green County's median, 2.1 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.1 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. Green County's median reported result, 2023.
The data
Green County, At a glance
Green County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Green 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 Green County, 2023
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 59.5% |
| 2015 | 54.4% |
| 2016 | 54.0% |
| 2017 | 55.8% |
| 2019 | 65.7% |
| 2020 | 60.8% |
| 2021 | 57.1% |
| 2022 | 66.5% |
| 2023 | 33.6% |
2023: 33.6%. Across these years the share ran from 33.6% to 66.5%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 235 tests reported to CDC for Green County over 2023, 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: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).
Green County, Compared
Green County radon figures, compared
Calculated by Radon411In Green County, about 3 in 10 reported tests in 2023 (79 of 235) were at or above EPA's action level. Against the national pool of 33.4%, the gap is 0.2 points higher. Across 72 Wisconsin counties pooled together, 35.7% of tests reached that level, so Green County runs 2.1 points below its state.
Of 4 neighbours with a figure, all 4 reported a larger share at or above 4 pCi/L; the spread is 34.9% (Dane County) to 61.0% (Iowa County). By share, Green County is 44th of 69 Wisconsin counties with 30 or more tests for the same period.
Year by year, 2014 opened at 59.5% and 2023 closed at 33.6% (down 25.9 points), with 2022 the high at 66.5%. Half the tests came in under 2.1 pCi/L and half over it; the single highest reached 147.9 pCi/L. Below the action level, 116 tests (49.4%) came in under 2 pCi/L, against 41.4% statewide, and 40 tests (17.0%) fell between 2 and 4, against 23.0% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 33.6% share point the same way here. USGS geology rates 100% of the county's land high radon potential.
The busiest year on file was 2023, with 235 tests reported; the quietest, 2021, had 70.
Green CountyWisconsin, pooled
| Year | Tests | Green County, at or above 4 pCi/L | Wisconsin, pooled |
|---|---|---|---|
| 2014 | 84 | 59.5% | 51.1% |
| 2015 | 79 | 54.4% | 51.6% |
| 2016 | 87 | 54.0% | 45.2% |
| 2017 | 77 | 55.8% | 44.8% |
| 2019 | 70 | 65.7% | 42.9% |
| 2020 | 97 | 60.8% | 27.0% |
| 2021 | 70 | 57.1% | 39.9% |
| 2022 | 173 | 66.5% | 42.9% |
| 2023 | 235 | 33.6% | 35.7% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Green County, Geology
The ground under Green County
PredictedUSGS's geologic map puts all of Green County's mapped land in one class: high radon potential. The map puts 75.3% of Green County in the area it calls Eastern Ridges and Lowlands and 23.9% in Driftless Area, with one smaller area beside them. USGS gives both 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 |
|---|---|---|---|---|
| Eastern Ridges and Lowlands | Glacial deposits derived from Ordovician carbonate rocks. | High | 12 | 75.3% |
| Driftless Area | Cambrian sandstone and Ordovician limestone and dolostone. | High | 12 | 23.9% |
| Galesburg Plain | Illinoian glacial deposits and loess over Paleozoic sedimentary rocks. | High | 13 | 0.7% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Green County beside the ground around it
Green County has more high-potential ground than Wisconsin as a whole: 100% of its land against 34.8%. Of the 6 counties that border it, none has as large a share of high-potential ground; Lafayette County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Green County, Local resources
Radon testing and mitigation in Green County
- Wisconsin's radon programWisconsin Department of Health ServicesWisconsin's radon program does not license radon professionals and offers free or discounted test kits, and answers questions about testing and mitigation in Wisconsin.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
We recommend starting with your regional Radon Information Center since many centers provide test kits for free or reduced cost, and often with laboratory fees covered.
- Compare kits
- Professionals in Wisconsin19 professionals are listed in Wisconsin.
What Wisconsin's program says
- Phone
- 1-888-569-7236
- DHSRadon@dhs.wisconsin.gov
- Licensing of radon professionals
The State of Wisconsin does not require contractors performing radon measurement or mitigation work to be state licensed or nationally certified.
What it means
Green County, Questions
Questions about radon in Green County
Are radon levels high in Green County?
In 2023, 33.6% of the radon tests reported to CDC for Green County, Wisconsin were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.1 pCi/L. Of 69 Wisconsin counties with 30 or more tests for the same period, 43 reported a higher share; pooled, the state comes to 35.7%.
Which counties border Green County?
Green County borders 6 counties: Stephenson County, IL, Dane County, WI, Lafayette County, WI, Rock County, WI, Winnebago County, IL and Iowa County, WI.
Products
Green County, Products
Testing a home in Green County
In Green County, 33.6% of 235 tests reported to CDC in 2023 reached 4 pCi/L, against 35.7% pooled across Wisconsin. In Zone 1 the year-round level in Green 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
Monitor
EcoQube Wi-Fi continuous radon monitor
- C-NRPP 2024/25: Approved
- Plug-in
- Wi-Fi
- App only
Method: Ion chamber
First reading: Within 10 minutes
Short-term kit
Air Chek Short-Term radon test kit you hang, lab fee included
- Lab fee included
In home: 72 to 168 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Green County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Green County
Explore
Green County, Bordering counties
Counties bordering Green County
Calculated by Radon411- Radon levels in Iowa County, WIEPA zone 1
61.0%at or above 4 pCi/L
Median 4.8 pCi/L · 146 tests · 27.4 points above Green County
- Radon levels in Lafayette County, WIEPA zone 1
52.2%at or above 4 pCi/L
Median 4.2 pCi/L · 46 tests · 18.6 points above Green County
- Radon levels in Rock County, WIEPA zone 1
49.9%at or above 4 pCi/L
Median 3.9 pCi/L · 451 tests · 16.3 points above Green County
- Radon levels in Dane County, WIEPA zone 1
34.9%at or above 4 pCi/L
Median 2.5 pCi/L · 2,887 tests · 1.3 points above Green County
- Radon levels in Stephenson County, ILEPA zone 1
No CDC figure for 2023; its page reads it against its own neighbours.
- Radon levels in Winnebago County, ILEPA zone 1
No CDC figure for 2023; its page reads it against its own neighbours.
Green County, Cities and towns
Cities and towns in Green County
The Census Bureau estimates 37,227 residents in Green County for July 1, 2025, 188 more than in 2020 (+0.5%). That works out to 64 people per square mile of land. Its largest town, Monroe, has 10,581 residents, 28.4% of the total. Testing is reported here more often than across the state: CDC's 235 reported tests for 2023 come to 6.3 for every 1,000 residents (2025 estimate), against 3.5 for Wisconsin.
From Monroe to Browntown, CDC publishes no figure by town: each reads Green County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Monroe | 10,581 | −0.5% | 28.4% |
| Brodheadextends beyond Green County | 3,214 | −1.5% | Counted whole |
| Bellevilleextends beyond Green County | 2,705 | +7.9% | Counted whole |
| New Glarus | 2,266 | −0.6% | 6.1% |
| Brooklynextends beyond Green County | 1,547 | +1.6% | Counted whole |
| Monticello | 1,173 | −1.0% | 3.2% |
| Albany | 1,089 | −1.7% | 2.9% |
| Browntown | 242 | Level | 0.7% |
8 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 Green County is counted whole, so it has no share.
Green County, Homes
Homes in Green County
Green County is a place of houses on their own lots: 77% of its 16,382 homes are detached single-family houses, against 66% across Wisconsin. Half of its homes were built before 1971, close to Wisconsin's 1975: 40% date from before 1960 and 17% from 2000 or later. Owners live in 75% of the occupied homes (Wisconsin: 68%), so for most households a test and a fix are their own to order.
| Homes | Green County | Wisconsin |
|---|---|---|
| Housing units | 16,382 | 2,750,750 |
| Detached houses | 77% | 66% |
| In buildings of 5 or more | 9% | 17% |
| Mobile homes | 4% | 3% |
| Built before 1960 | 40% | 34% |
| Built since 2000 | 17% | 20% |
| Middle year built | 1971 | 1975 |
| Owner-occupied | 75% | 68% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.