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 Grant County, Wisconsin
EPA puts Grant County in Zone 1, its highest radon zone, and high results are common there: 48.3% of the 323 radon tests reported to CDC (2023) came back 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
48.3%
12.6 pts above WI
- Grant
- 48.3%
- Wisconsin
- 35.7%
323 tests, 2023
Median result
3.5pCi/L
Below action level
- Grant
- 3.5 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2023
Tests reported
323
20th of 69 by tests
- Grant
- 323
- 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
13 of 69
Top quarter
- Grant
- 48.3%
- Langlade
- 65.8%
By share, of 69 with 30+ tests
Read a result for Grant County
Starts at Grant County's median, 3.5 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 3.5 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. Grant County's median reported result, 2023.
The data
Grant County, At a glance
Grant County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Grant 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 Grant County, 2023
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 59.5% |
| 2015 | 55.4% |
| 2016 | 55.6% |
| 2017 | 44.3% |
| 2019 | 53.6% |
| 2020 | 54.6% |
| 2021 | 59.6% |
| 2022 | 62.5% |
| 2023 | 48.3% |
2023: 48.3%. Across these years the share ran from 44.3% to 62.5%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 323 tests reported to CDC for Grant 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).
Grant County, Compared
Grant County radon figures, compared
Calculated by Radon411In Grant County, about 5 in 10 reported tests in 2023 (156 of 323) were at or above EPA's action level. Against the national pool of 33.4%, the gap is 14.9 points higher. Across 72 Wisconsin counties pooled together, 35.7% of tests reached that level, so Grant County runs 12.6 points above its state.
Of 4 neighbours with a figure, 3 reported a larger share at or above 4 pCi/L and 1 a smaller one; the spread is 33.3% (Richland County) to 61.0% (Iowa County). By share, Grant County is 13th 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 48.3% (down 11.2 points), with 2022 the high at 62.5%. Half the tests came in under 3.5 pCi/L and half over it; the single highest reached 39.6 pCi/L. Below the action level, 122 tests (37.8%) came in under 2 pCi/L, against 41.4% statewide, and 45 tests (13.9%) fell between 2 and 4, against 23.0% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 48.3% share point the same way here. USGS geology rates 100% of the county's land high radon potential. CDC also counts 11 tests taken after mitigation in Grant County for the same period: tests in homes where a fix was already in.
The busiest year on file was 2023, with 323 tests reported; the quietest, 2021, had 151.
Grant CountyWisconsin, pooled
48.3% % of tests35.7% % of tests
| Year | Tests | Grant County, at or above 4 pCi/L | Wisconsin, pooled |
|---|---|---|---|
| 2014 | 222 | 59.5% | 51.1% |
| 2015 | 168 | 55.4% | 51.6% |
| 2016 | 189 | 55.6% | 45.2% |
| 2017 | 167 | 44.3% | 44.8% |
| 2019 | 252 | 53.6% | 42.9% |
| 2020 | 152 | 54.6% | 27.0% |
| 2021 | 151 | 59.6% | 39.9% |
| 2022 | 160 | 62.5% | 42.9% |
| 2023 | 323 | 48.3% | 35.7% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Grant County, Geology
The ground under Grant County
PredictedUSGS's geologic map puts all of Grant County's mapped land in one class: high radon potential. All of it lies in the area the map calls Driftless Area, to which USGS gives 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 |
|---|---|---|---|---|
| Driftless Area | Cambrian sandstone and Ordovician limestone and dolostone. | High | 12 | 99.7% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Grant County beside the ground around it
Grant County has more high-potential ground than Wisconsin as a whole: 100% of its land against 34.8%. Of the 7 counties that border it, none has as large a share of high-potential ground; Crawford County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Grant County, Local resources
Radon testing and mitigation in Grant 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
Grant County, Questions
Questions about radon in Grant County
Are radon levels high in Grant County?
In 2023, 48.3% of the radon tests reported to CDC for Grant County, Wisconsin were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.5 pCi/L. Of 69 Wisconsin counties with 30 or more tests for the same period, 12 reported a higher share; pooled, the state comes to 35.7%.
Which counties border Grant County?
Grant County borders 7 counties: Dubuque County, IA, Crawford County, WI, Clayton County, IA, Iowa County, WI, Lafayette County, WI, Richland County, WI and Jo Daviess County, IL.
Products
Grant County, Products
Testing a home in Grant County
In Grant County, 48.3% of 323 tests reported to CDC in 2023 reached 4 pCi/L, against 35.7% pooled across Wisconsin. In Zone 1 the year-round level in Grant 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
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
Short-term kit
RA400 short-term liquid scintillation radon test kit, lab fee included
- Lab fee included
Method: Liquid scintillation
In home: 48 to 96 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Grant County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Grant County
Explore
Grant County, Bordering counties
Counties bordering Grant 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 · 12.7 points above Grant County
- Radon levels in Crawford County, WIEPA zone 1
53.9%at or above 4 pCi/L
Median 4.4 pCi/L · 217 tests · 5.6 points above Grant County
- Radon levels in Lafayette County, WIEPA zone 1
52.2%at or above 4 pCi/L
Median 4.2 pCi/L · 46 tests · 3.9 points above Grant County
- Radon levels in Richland County, WIEPA zone 1
33.3%at or above 4 pCi/L
Median 2.9 pCi/L · 48 tests · 15.0 points below Grant County
- Radon levels in Dubuque County, IAEPA zone 1
No CDC figure for 2023; its page reads it against its own neighbours.
- Radon levels in Clayton County, IAEPA zone 1
No CDC figure for 2023; its page reads it against its own neighbours.
- Radon levels in Jo Daviess County, ILEPA zone 1
No CDC figure for 2023; its page reads it against its own neighbours.
Grant County, Cities and towns
Cities and towns in Grant County
The Census Bureau estimates 52,446 residents in Grant County for July 1, 2025, 457 more than in 2020 (+0.9%). That works out to 46 people per square mile of land. Its largest town, Platteville, has 11,815 residents, 22.5% of the total. Testing is reported here more often than across the state: CDC's 323 reported tests for 2023 come to 6.2 for every 1,000 residents (2025 estimate), against 3.5 for Wisconsin.
From Platteville to Woodman, CDC publishes no figure by town: each reads Grant County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Platteville | 11,815 | −0.2% | 22.5% |
| Lancaster | 4,031 | +2.5% | 7.7% |
| Boscobel | 3,250 | −1.4% | 6.2% |
| Fennimore | 2,775 | +0.5% | 5.3% |
| Cuba Cityextends beyond Grant County | 2,103 | −1.7% | Counted whole |
| Muscodaextends beyond Grant County | 1,304 | +0.2% | Counted whole |
| Hazel Greenextends beyond Grant County | 1,173 | −0.3% | Counted whole |
| Dickeyville | 1,085 | +6.8% | 2.1% |
| Cassville | 758 | −1.8% | 1.4% |
| Bloomington | 754 | +0.8% | 1.4% |
| Montfortextends beyond Grant County | 734 | +3.1% | Counted whole |
| Potosi | 649 | +0.8% | 1.2% |
- Livingston (part)
- Blue River
- Bagley
- Tennyson
- Mount Hope
- Patch Grove
- Woodman
19 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 Grant County is counted whole, so it has no share.
Grant County, Homes
Homes in Grant County
Grant County is a place of houses on their own lots: 75% of its 22,192 homes are detached single-family houses, against 66% across Wisconsin. Half of its homes were built before 1973, close to Wisconsin's 1975: 35% date from before 1960 and 18% from 2000 or later. 69% of occupied homes are lived in by their owner (Wisconsin: 68%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Grant County | Wisconsin |
|---|---|---|
| Housing units | 22,192 | 2,750,750 |
| Detached houses | 75% | 66% |
| In buildings of 5 or more | 11% | 17% |
| Mobile homes | 5% | 3% |
| Built before 1960 | 35% | 34% |
| Built since 2000 | 18% | 20% |
| Middle year built | 1973 | 1975 |
| Owner-occupied | 69% | 68% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.