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 Brown County, Illinois
EPA puts Brown County in Zone 1, its highest radon zone, and only 18 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
41.0%
2.7 pts below IL
- Brown
- 41.0%
- Illinois
- 43.7%
39 tests, 2007 to 2016
Median result
3.2pCi/L
Below action level
- Brown
- 3.2 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2007 to 2016
Tests reported
39
89th of 92 by tests
- Brown
- 39
- Cook
- 13,699
Reported to CDC before any fix, 2007 to 2016
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
53 of 92
Middle half
- Brown
- 41.0%
- Stark
- 79.4%
By share, of 92 with 30+ tests
Read a result for Brown County
Starts at Brown County's median, 3.2 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 3.2 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. Brown County's median reported result, 2007 to 2016.
The data
Brown County, At a glance
Brown County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Brown 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 Brown County, 2017
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 75.0% |
| 2015 | 50.0% |
| 2017 | 50.0% |
2017: 50.0%. Across these years the share ran from 50.0% to 75.0%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
Only 18 tests were reported to CDC for Brown 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).
Brown County, Compared
Brown County radon figures, compared
Calculated by Radon411In Brown County, about 4 in 10 reported tests over the 2007 to 2016 laboratory totals (16 of 39) were at or above EPA's action level. Against the national pool of 35.8%, the gap is 5.2 points higher. Across 102 Illinois counties pooled together, 43.7% of tests reached that level, so Brown County runs 2.7 points below its state.
The newest figure, in 2017, counts only 18 tests (50.0% at or above 4 pCi/L), too few to compare, so this reading uses the 39-test figure.
Of 5 neighbours with a figure, all 5 reported a larger share at or above 4 pCi/L; the spread is 42.9% (Cass County) to 65.4% (Morgan County). By share, Brown County is 53rd of 92 Illinois counties with 30 or more tests for the same period.
Half the tests came in under 3.2 pCi/L and half over it; the single highest reached 26.8 pCi/L. Below the action level, 13 tests (33.3%) came in under 2 pCi/L, against 31.2% statewide, and 10 tests (25.6%) fell between 2 and 4, against 25.1% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 41.0% 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 24 tests reported; the quietest, 2015, had 12.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Brown County, Geology
The ground under Brown County
PredictedUSGS's geologic map puts all of Brown 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.
Brown County beside the ground around it
Brown 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; Cass County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Brown County, Local resources
Radon testing and mitigation in Brown County
Listed radon businesses with an address in Brown 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: Versailles
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
Brown County, Questions
Questions about radon in Brown County
Are radon levels high in Brown County?
In 2017, 50.0% of the radon tests reported to CDC for Brown County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.0 pCi/L. Of 92 Illinois counties with 30 or more tests for the same period, 52 reported a higher share; pooled, the state comes to 43.7%.
Which counties border Brown County?
Brown County borders 5 counties: Schuyler County, Adams County, Cass County, Pike County and Morgan County.
Products
Brown County, Products
Testing a home in Brown County
In Brown County, 41.0% of 39 tests reported to CDC over the 2007 to 2016 laboratory totals reached 4 pCi/L, against 43.7% pooled across Illinois. In Zone 1 the year-round level in Brown 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
MonitorAranet
Radon One battery digital radon monitor with an e-ink screen
- C-NRPP 2024/25: Not included
- Battery
- Bluetooth
- Alarm
- Screen, app
Method: Ion chamber
First reading: Within 10 minutes
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
Brown County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Brown County
Explore
Brown County, Bordering counties
Counties bordering Brown County
Calculated by Radon411- Radon levels in Morgan CountyEPA zone 1
65.4%at or above 4 pCi/L
Median 5.8 pCi/L · 182 tests · 24.4 points above Brown County
- Radon levels in Schuyler CountyEPA zone 1
57.1%at or above 4 pCi/L
Median 5.3 pCi/L · 49 tests · 16.1 points above Brown County
- Radon levels in Adams CountyEPA zone 1
56.7%at or above 4 pCi/L
Median 4.7 pCi/L · 3,261 tests · 15.7 points above Brown County
- Radon levels in Pike CountyEPA zone 1
45.8%at or above 4 pCi/L
Median 3.8 pCi/L · 96 tests · 4.8 points above Brown County
- Radon levels in Cass CountyEPA zone 1
42.9%at or above 4 pCi/L
Median 3.3 pCi/L · 49 tests · 1.9 points above Brown County
Brown County, Cities and towns
Cities and towns in Brown County
The Census Bureau estimates 6,401 residents in Brown County for July 1, 2025, 169 more than in 2020 (+2.7%). That works out to 21 people per square mile of land. Its largest town, Mount Sterling, has 2,155 residents, 33.7% of the total. Together its 4 incorporated places hold 43.3% of those residents; the other 56.7% live outside any of them. CDC's 39 reported tests for 2007 to 2016 work out to 6.1 per 1,000 residents (2025 estimate), close to Illinois' 8.3.
From Mount Sterling to Ripley, CDC publishes no figure by town: each reads Brown County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Mount Sterling | 2,155 | +7.9% | 33.7% |
| Versailles | 446 | +0.5% | 7.0% |
| Mound Station | 117 | +0.9% | 1.8% |
| Ripley | 51 | +4.1% | 0.8% |
4 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).
Brown County, Homes
Homes in Brown County
Brown County is a place of houses on their own lots: 81% of its 2,321 homes are detached single-family houses, against 58% across Illinois. The homes are older than Illinois' as a whole: half were built before 1960 (1970 for Illinois), and 50% date from before 1960. 74% 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 | Brown County | Illinois |
|---|---|---|
| Housing units | 2,321 | 5,443,501 |
| Detached houses | 81% | 58% |
| In buildings of 5 or more | 7% | 22% |
| Mobile homes | 7% | 2% |
| Built before 1960 | 50% | 38% |
| Built since 2000 | 12% | 16% |
| Middle year built | 1960 | 1970 |
| Owner-occupied | 74% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.