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 Grundy County, Illinois
EPA puts Grundy County in Zone 1, its highest radon zone, and 32.3% of its 390 reported radon tests (2017) 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
32.3%
1.4 pts below IL
- Grundy
- 32.3%
- Illinois
- 33.7%
390 tests, 2017
Median result
2.4pCi/L
Below action level
- Grundy
- 2.4 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2017
Tests reported
390
31st of 70 by tests
- Grundy
- 390
- Cook
- 26,937
Reported to CDC before any fix, 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 Illinois
55 of 70
Lowest quarter
- Grundy
- 32.3%
- Stark
- 69.2%
By share, of 70 with 30+ tests
Read a result for Grundy County
Starts at Grundy County's median, 2.4 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.4 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. Grundy County's median reported result, 2017.
The data
Grundy County, At a glance
Grundy County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Grundy 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 Grundy County, 2017
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 45.2% |
| 2015 | 50.6% |
| 2016 | 0.0% |
| 2017 | 32.3% |
2017: 32.3%. Across these years the share ran from 0.0% to 50.6%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 390 tests reported to CDC for Grundy County over 2017, 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: 2017. Measured data period: 2005 to 2017 (every CDC figure on file).
Grundy County, Compared
Grundy County radon figures, compared
Calculated by Radon411In Grundy County, about 3 in 10 reported tests in 2017 (126 of 390) were at or above EPA's action level. Against the national pool of 31.7%, the gap is 0.6 points higher. Across 93 Illinois counties pooled together, 33.7% of tests reached that level, so Grundy County runs 1.4 points below its state.
Of 5 neighbours with a figure, 4 reported a larger share at or above 4 pCi/L and 1 a smaller one; the spread is 31.6% (Kankakee County) to 61.7% (Livingston County). By share, Grundy County is 55th of 70 Illinois counties with 30 or more tests for the same period.
Year by year, 2014 opened at 45.2% and 2017 closed at 32.3% (down 12.9 points), with 2015 the high at 50.6%. Half the tests came in under 2.4 pCi/L and half over it; the single highest reached 27.8 pCi/L. Below the action level, 150 tests (38.5%) came in under 2 pCi/L, against 37.7% statewide, and 114 tests (29.2%) fell between 2 and 4, against 28.6% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 32.3% share point the same way here. USGS geology rates 100% of the county's land high radon potential.
The busiest year on file was 2014, with 405 tests reported; the quietest, 2016, had 3.
Grundy CountyIllinois, pooled
| Year | Tests | Grundy County, at or above 4 pCi/L | Illinois, pooled |
|---|---|---|---|
| 2014 | 405 | 45.2% | 37.8% |
| 2015 | 249 | 50.6% | 36.6% |
| 2017 | 390 | 32.3% | 33.7% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Grundy County, Geology
The ground under Grundy County
PredictedUSGS's geologic map puts all of Grundy County's mapped land in one class: high radon potential. All of it lies in the area the map calls Bloomington Ridged Plain, to which USGS gives a radon index of 13, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Bloomington Ridged Plain | Wisconsinan glacial deposits and loess over Paleozoic sedimentary rocks. | High | 13 | 100% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Grundy County beside the ground around it
Grundy County has more high-potential ground than Illinois as a whole: 100% of its land against 64.5%. Of the 5 counties that border it, none has as large a share of high-potential ground; Kendall County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Grundy County, Local resources
Radon testing and mitigation in Grundy County
Listed radon businesses with an address in Grundy County:
- IEMA-OHS Radon ProgramIEMA-OHS Radon Program, run by Illinois Emergency Management Agency and Office of Homeland Security, licenses or certifies radon professionals and states the rule for disclosing radon when a home is sold, and answers questions about testing and mitigation in Illinois.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsAsk the program whether it has free or discounted kits, or compare kits you can buy.
- Compare kits
- Professionals in Illinois339 professionals are listed in Illinois.
Listed radon professionals by town: Seneca, Verona
What Illinois's program says
- Phone
- (800) 325-1245
- Licensing of radon professionals
The Agency also licenses and regulates the individuals who provide radon measurement and mitigation to the public.
- Disclosure when a home is sold or rented
Illinois Radon Awareness Act - This is the legislation that requires the seller to provide to the buyer of any interest in residential real property the IEMA-OHS pamphlet entitled "Radon Testing Guidelines for Real Estate Transactions" and the Illinois Disclosure of Information on Radon Hazards.
What it means
Grundy County, Questions
Questions about radon in Grundy County
Are radon levels high in Grundy County?
In 2017, 32.3% of the radon tests reported to CDC for Grundy County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.4 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 54 reported a higher share; pooled, the state comes to 33.7%.
Which counties border Grundy County?
Grundy County borders 5 counties: Kendall County, LaSalle County, Will County, Kankakee County and Livingston County.
Products
Grundy County, Products
Testing a home in Grundy County
In Grundy County, 32.3% of 390 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 1 the year-round level in Grundy 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
RadonScan-Plus USB-powered radon monitor with Wi-Fi
- C-NRPP 2024/25: Not included
- Plug-in
- Wi-Fi
- Alarm
- Screen, app
First reading: Within 5 minutes
Short-term kit
RA100 short-term liquid scintillation radon test kit
- Lab fee extra
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
Grundy County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Grundy County
Explore
Grundy County, Bordering counties
Counties bordering Grundy County
Calculated by Radon411- Radon levels in Livingston CountyEPA zone 1
61.7%at or above 4 pCi/L
Median 5.3 pCi/L · 345 tests · 29.4 points above Grundy County
- Radon levels in LaSalle CountyEPA zone 1
45.8%at or above 4 pCi/L
Median 3.6 pCi/L · 1,002 tests · 13.5 points above Grundy County
- Radon levels in Will CountyEPA zone 2
40.0%at or above 4 pCi/L
Median 3.1 pCi/L · 10,776 tests · 7.7 points above Grundy County
- Radon levels in Kendall CountyEPA zone 1
35.0%at or above 4 pCi/L
Median 2.8 pCi/L · 3,045 tests · 2.7 points above Grundy County
- Radon levels in Kankakee CountyEPA zone 2
31.6%at or above 4 pCi/L
Median 2.7 pCi/L · 522 tests · 0.7 points below Grundy County
Grundy County, Cities and towns
Cities and towns in Grundy County
The Census Bureau estimates 54,052 residents in Grundy County for July 1, 2025, 1,514 more than in 2020 (+2.9%). That works out to 129 people per square mile of land. Its largest town, Morris, has 14,669 residents, 27.1% of the total. Reported testing is thin here: 390 tests over 2017, or 7.2 for every 1,000 residents (2025 estimate), where Illinois as a whole comes to 10.9.
From Morris to East Brooklyn, CDC publishes no figure by town: each reads Grundy County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Morris | 14,669 | +3.1% | 27.1% |
| Channahonextends beyond Grundy County | 14,530 | +7.9% | Counted whole |
| Minookaextends beyond Grundy County | 12,899 | +1.2% | Counted whole |
| Braidwoodextends beyond Grundy County | 6,259 | +1.1% | Counted whole |
| Coal Cityextends beyond Grundy County | 5,831 | +2.4% | Counted whole |
| Dwightextends beyond Grundy County | 4,005 | −0.5% | Counted whole |
| Diamondextends beyond Grundy County | 2,714 | +3.1% | Counted whole |
| Senecaextends beyond Grundy County | 2,310 | −1.6% | Counted whole |
| Gardner | 1,366 | +0.5% | 2.5% |
| Mazon | 984 | +0.3% | 1.8% |
| Bracevilleextends beyond Grundy County | 732 | +1.4% | Counted whole |
| South Wilmington | 719 | +1.7% | 1.3% |
- Godley (part)
- Carbon Hill
- Verona
- Kinsman
- East Brooklyn
17 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 Grundy County is counted whole, so it has no share.
Grundy County, Homes
Homes in Grundy County
Of Grundy County's 21,324 homes, 71% are detached houses, against 58% across Illinois; 8% are in buildings of five or more homes. Much of Grundy County is recent building: 36% of its homes have gone up since 2000 and the middle year built is 1990, against 1970 for Illinois. Owners live in 76% of the occupied homes (Illinois: 67%), so for most households a test and a fix are their own to order.
| Homes | Grundy County | Illinois |
|---|---|---|
| Housing units | 21,324 | 5,443,501 |
| Detached houses | 71% | 58% |
| In buildings of 5 or more | 8% | 22% |
| Mobile homes | 4% | 2% |
| Built before 1960 | 20% | 38% |
| Built since 2000 | 36% | 16% |
| Middle year built | 1990 | 1970 |
| Owner-occupied | 76% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.