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 Cass County, Illinois
EPA puts Cass County in Zone 1, its highest radon zone, and only 24 radon tests from it are on file with CDC (2017). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Share at 4+ pCi/L
38.5%
4.6 pts below IL
- Cass
- 38.5%
- Illinois
- 43.1%
52 tests, 2008 to 2017
Median result
3.0pCi/L
Below action level
- Cass
- 3.0 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
52
84th of 93 by tests
- Cass
- 52
- Cook
- 14,199
Reported to CDC before any fix, 2008 to 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
59 of 93
Middle half
- Cass
- 38.5%
- Stark
- 80.5%
By share, of 93 with 30+ tests
Read a result for Cass County
Starts at Cass County's median, 3.0 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 3.0 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. Cass County's median reported result, 2008 to 2017.
The data
Cass County, At a glance
Cass County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Cass 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 Cass County, 2017
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 57.1% |
| 2015 | 50.0% |
| 2017 | 25.0% |
2017: 25.0%. Across these years the share ran from 25.0% to 57.1%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
Only 24 tests were reported to CDC for Cass County over 2017, 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: 2017. Measured data period: 2005 to 2017 (every CDC figure on file).
Cass County, Compared
Cass County radon figures, compared
Calculated by Radon411In Cass County, about 4 in 10 reported tests over the 2008 to 2017 laboratory totals (20 of 52) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 2.8 points higher. Across 102 Illinois counties pooled together, 43.1% of tests reached that level, so Cass County runs 4.6 points below its state.
The newest figure, in 2017, counts only 24 tests (25.0% at or above 4 pCi/L), too few to compare, so this reading uses the 52-test figure.
Of 6 neighbours with a figure, 5 reported a larger share at or above 4 pCi/L and 1 a smaller one; the spread is 37.8% (Brown County) to 64.5% (Morgan County). By share, Cass County is 59th of 93 Illinois counties with 30 or more tests for the same period.
Half the tests came in under 3.0 pCi/L and half over it; the single highest reached 16.2 pCi/L. Below the action level, 21 tests (40.4%) came in under 2 pCi/L, against 31.6% statewide, and 11 tests (21.2%) fell between 2 and 4, against 25.3% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 38.5% 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 42 tests reported; the quietest, 2015, had 18.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Cass County, Geology
The ground under Cass County
PredictedUSGS's geologic map puts all of Cass County's mapped land in one class: high radon potential. All of it lies in the area the map calls Galesburg 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 |
|---|---|---|---|---|
| Galesburg Plain | Illinoian 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.
Cass County beside the ground around it
Cass County has more high-potential ground than Illinois as a whole: 100% of its land against 64.5%. Of the 6 counties that border it, none has as large a share of high-potential ground; Brown County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Cass County, Local resources
Radon testing and mitigation in Cass 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.
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
Cass County, Questions
Questions about radon in Cass County
Are radon levels high in Cass County?
In 2017, 25.0% of the radon tests reported to CDC for Cass County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.9 pCi/L. Of 93 Illinois counties with 30 or more tests for the same period, 58 reported a higher share; pooled, the state comes to 43.1%.
Which counties border Cass County?
Cass County borders 6 counties: Morgan County, Schuyler County, Menard County, Brown County, Mason County and Sangamon County.
Products
Cass County, Products
Testing a home in Cass County
In Cass County, 38.5% of 52 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 43.1% pooled across Illinois. In Zone 1 the year-round level in Cass 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
RM-63Pro rechargeable radon monitor with a touchscreen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
Short-term kitKidde
442020 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 3 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Cass County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Cass County
Explore
Cass County, Bordering counties
Counties bordering Cass County
Calculated by Radon411- Radon levels in Morgan CountyEPA zone 1
64.5%at or above 4 pCi/L
Median 5.8 pCi/L · 169 tests · 26.0 points above Cass County
- Radon levels in Sangamon CountyEPA zone 1
52.2%at or above 4 pCi/L
Median 4.2 pCi/L · 2,962 tests · 13.7 points above Cass County
- Radon levels in Menard CountyEPA zone 1
51.3%at or above 4 pCi/L
Median 4.2 pCi/L · 117 tests · 12.8 points above Cass County
- Radon levels in Schuyler CountyEPA zone 1
43.9%at or above 4 pCi/L
Median 3.8 pCi/L · 41 tests · 5.4 points above Cass County
- Radon levels in Mason CountyEPA zone 1
43.1%at or above 4 pCi/L
Median 3.5 pCi/L · 102 tests · 4.6 points above Cass County
- Radon levels in Brown CountyEPA zone 1
37.8%at or above 4 pCi/L
Median 2.9 pCi/L · 37 tests · 0.7 points below Cass County
Cass County, Cities and towns
Cities and towns in Cass County
About 12,463 people live in Cass County by the Census Bureau's estimate for July 1, 2025, 515 fewer than in 2020 (−4.0%). That works out to 33 people per square mile of land. Its largest town, Beardstown, has 5,691 residents, 45.7% of the total. Together its 5 incorporated places hold 73.5% of those residents; the other 26.5% live outside any of them. Reported testing is thin here: 52 tests over 2008 to 2017, or 4.2 for every 1,000 residents (2025 estimate), where Illinois as a whole comes to 8.6.
From Beardstown to Arenzville, CDC publishes no figure by town: each reads Cass County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Beardstown | 5,691 | −3.9% | 45.7% |
| Virginia | 1,442 | −4.4% | 11.6% |
| Ashland | 1,162 | −4.4% | 9.3% |
| Chandlerville | 508 | −3.6% | 4.1% |
| Arenzville | 355 | −4.3% | 2.8% |
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).
Cass County, Homes
Homes in Cass County
Cass County is a place of houses on their own lots: 79% of its 5,665 homes are detached single-family houses, against 58% across Illinois. Half of its homes were built before 1967, close to Illinois' 1970: 42% date from before 1960 and 11% from 2000 or later. 75% of occupied homes are lived in by their owner (Illinois: 67%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Cass County | Illinois |
|---|---|---|
| Housing units | 5,665 | 5,443,501 |
| Detached houses | 79% | 58% |
| In buildings of 5 or more | 4% | 22% |
| Mobile homes | 11% | 2% |
| Built before 1960 | 42% | 38% |
| Built since 2000 | 11% | 16% |
| Middle year built | 1967 | 1970 |
| Owner-occupied | 75% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.