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 Mason County, Illinois
EPA puts Mason County in Zone 1, its highest radon zone, and 21.4% of its 42 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
21.4%
12.3 pts below IL
- Mason
- 21.4%
- Illinois
- 33.7%
42 tests, 2017
Median result
2.8pCi/L
Below action level
- Mason
- 2.8 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2017
Tests reported
42
66th of 70 by tests
- Mason
- 42
- 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
64 of 70
Lowest quarter
- Mason
- 21.4%
- Stark
- 69.2%
By share, of 70 with 30+ tests
Read a result for Mason County
Starts at Mason County's median, 2.8 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.8 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. Mason County's median reported result, 2017.
The data
Mason County, At a glance
Mason County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Mason 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 Mason County, 2017
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 50.0% |
| 2015 | 71.4% |
| 2017 | 21.4% |
2017: 21.4%. Across these years the share ran from 21.4% to 71.4%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 42 tests reported to CDC for Mason 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).
Mason County, Compared
Mason County radon figures, compared
Calculated by Radon411Mason County's 42 reported tests in 2017 had a middle value of 2.8 pCi/L and a maximum of 19.1 pCi/L, and 21.4% reached 4 pCi/L. Illinois as a whole (93 Illinois counties, pooled) comes to 33.7%: 12.3 points higher than here.
Among its state's counties it ranks 64th of 70 Illinois counties with 30 or more tests for the same period. Statewide for the same period, Stark County reported the highest share (69.2%) and Williamson County the lowest (8.4%).
Below the action level, 9 tests (21.4%) came in under 2 pCi/L, against 37.7% statewide, and 24 tests (57.1%) fell between 2 and 4, against 28.6% statewide. The busiest year on file was 2014, with 48 tests reported; the quietest, 2015, had 21.
EPA's 1993 zone map puts Mason County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 100% of the county's land high radon potential.
Next door, the shares run from 45.8% in Logan County to 64.6% in Fulton County.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Mason County, Geology
The ground under Mason County
PredictedUSGS's geologic map puts all of Mason 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.
Mason County beside the ground around it
Mason 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; Cass County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Mason County, Local resources
Radon testing and mitigation in Mason 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
Mason County, Questions
Questions about radon in Mason County
Are radon levels high in Mason County?
In 2017, 21.4% of the radon tests reported to CDC for Mason County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.8 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 63 reported a higher share; pooled, the state comes to 33.7%.
Which counties border Mason County?
Mason County borders 6 counties: Menard County, Fulton County, Tazewell County, Cass County, Logan County and Schuyler County.
Products
Mason County, Products
Testing a home in Mason County
In Mason County, 21.4% of 42 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 1 the year-round level in Mason 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
MonitorAEGTEST
HOUND-3699 radon monitor with a 2.1-inch touchscreen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
First reading: Within 1 hour
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
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Mason County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Mason County
Explore
Mason County, Bordering counties
Counties bordering Mason County
Calculated by Radon411- Radon levels in Fulton CountyEPA zone 1
64.6%at or above 4 pCi/L
Median 5.8 pCi/L · 144 tests · 43.2 points above Mason County
- Radon levels in Menard CountyEPA zone 1
51.8%at or above 4 pCi/L
Median 4.3 pCi/L · 168 tests · 30.4 points above Mason County
- Radon levels in Tazewell CountyEPA zone 1
46.4%at or above 4 pCi/L
Median 3.6 pCi/L · 2,724 tests · 25.0 points above Mason County
- Radon levels in Logan CountyEPA zone 1
45.8%at or above 4 pCi/L
Median 3.4 pCi/L · 72 tests · 24.4 points above Mason County
- Radon levels in Cass CountyEPA zone 1
25.0%at or above 4 pCi/L
Median 2.9 pCi/L · 24 tests · 3.6 points above Mason County
- Radon levels in Schuyler CountyEPA zone 1
No CDC figure for 2017; its page reads it against its own neighbours.
Mason County, Cities and towns
Cities and towns in Mason County
About 12,411 people live in Mason County by the Census Bureau's estimate for July 1, 2025, 639 fewer than in 2020 (−4.9%). That works out to 23 people per square mile of land. Its largest town, Havana, has 2,799 residents, 22.6% of the total. Reported testing is thin here: 42 tests over 2017, or 3.4 for every 1,000 residents (2025 estimate), where Illinois as a whole comes to 10.9.
From Havana to Topeka, CDC publishes no figure by town: each reads Mason County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Havana | 2,799 | −5.2% | 22.6% |
| Mason City | 1,956 | −5.4% | 15.8% |
| Manito | 1,473 | −4.9% | 11.9% |
| San Joseextends beyond Mason County | 460 | −4.2% | Counted whole |
| Easton | 298 | −6.0% | 2.4% |
| Bath | 262 | −4.0% | 2.1% |
| Kilbourne | 256 | −4.1% | 2.1% |
| Forest City | 211 | −4.1% | 1.7% |
| Topeka | 50 | −5.7% | 0.4% |
9 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 Mason County is counted whole, so it has no share.
Mason County, Homes
Homes in Mason County
Mason County is a place of houses on their own lots: 90% of its 6,615 homes are detached single-family houses, against 58% across Illinois. The homes are older than Illinois' as a whole: half were built before 1962 (1970 for Illinois), and 48% date from before 1960. Owners live in 81% of the occupied homes (Illinois: 67%), so for most households a test and a fix are their own to order.
| Homes | Mason County | Illinois |
|---|---|---|
| Housing units | 6,615 | 5,443,501 |
| Detached houses | 90% | 58% |
| In buildings of 5 or more | 3% | 22% |
| Mobile homes | 4% | 2% |
| Built before 1960 | 48% | 38% |
| Built since 2000 | 9% | 16% |
| Middle year built | 1962 | 1970 |
| Owner-occupied | 81% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.