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 Warren County, Illinois
EPA puts Warren County in Zone 1, its highest radon zone, and high results are common there: 50.0% of the 42 radon tests reported to CDC (2017) 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
50.0%
16.3 pts above IL
- Warren
- 50.0%
- Illinois
- 33.7%
42 tests, 2017
Median result
3.6pCi/L
Below action level
- Warren
- 3.6 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2017
Tests reported
42
65th of 70 by tests
- Warren
- 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
21 of 70
Middle half
- Warren
- 50.0%
- Stark
- 69.2%
By share, of 70 with 30+ tests
Read a result for Warren County
Starts at Warren County's median, 3.6 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 3.6 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. Warren County's median reported result, 2017.
The data
Warren County, At a glance
Warren County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Warren 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 Warren County, 2017
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 75.0% |
| 2015 | 66.7% |
| 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
These are the 42 tests reported to CDC for Warren 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).
Warren County, Compared
Warren County radon figures, compared
Calculated by Radon411More than half: 50.0% of the 42 radon tests reported to CDC for Warren County in 2017 read at least 4 pCi/L. That places it 21st of 70 Illinois counties with 30 or more tests for the same period. That is 16.3 points above the 33.7% pooled from 93 Illinois counties.
The median result, 3.6 pCi/L, sits between 2 and EPA's 4 pCi/L action level, and the top reported result was 12.9 pCi/L. The rest split 14.3% under 2 pCi/L and 35.7% from 2 to 4 (Illinois: 37.7% and 28.6%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 50.0% share point the same way here.
All 4 of its bordering counties with figures ran higher, led by Mercer County at 68.2%; the lowest of them, McDonough County, reported 55.7%. Statewide for the same period, Stark County reported the highest share (69.2%) and Williamson County the lowest (8.4%).
The busiest year on file was 2014, with 72 tests reported; the quietest, 2015, had 27.
Nationally, every county with a figure for the same period pools to 31.7%; Warren County sits 18.3 points above it.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Warren County, Geology
The ground under Warren County
PredictedUSGS's geologic map puts all of Warren 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.
Warren County beside the ground around it
Warren 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; Fulton County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Warren County, Local resources
Radon testing and mitigation in Warren 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
Warren County, Questions
Questions about radon in Warren County
Are radon levels high in Warren County?
In 2017, 50.0% of the radon tests reported to CDC for Warren County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.6 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 20 reported a higher share; pooled, the state comes to 33.7%.
Which counties border Warren County?
Warren County borders 5 counties: Henderson County, Knox County, Mercer County, McDonough County and Fulton County.
Products
Warren County, Products
Testing a home in Warren County
In Warren County, 50.0% 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 Warren 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
Hello Radon C battery radon monitor with an e-ink screen
- C-NRPP 2024/25: Not included
- Battery
- Screen
Method: Alpha spectrometry
First reading: Within 24 hours
Short-term kitFirst Alert
RD1 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 2 to 4 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Warren County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Warren County
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Warren County, Bordering counties
Counties bordering Warren County
Calculated by Radon411- Radon levels in Mercer CountyEPA zone 1
68.2%at or above 4 pCi/L
Median 5.5 pCi/L · 66 tests · 18.2 points above Warren County
- Radon levels in Fulton CountyEPA zone 1
64.6%at or above 4 pCi/L
Median 5.8 pCi/L · 144 tests · 14.6 points above Warren County
- Radon levels in Knox CountyEPA zone 1
56.6%at or above 4 pCi/L
Median 4.7 pCi/L · 249 tests · 6.6 points above Warren County
- Radon levels in McDonough CountyEPA zone 1
55.7%at or above 4 pCi/L
Median 4.3 pCi/L · 210 tests · 5.7 points above Warren County
- Radon levels in Henderson CountyEPA zone 1
No CDC figure for 2017; its page reads it against its own neighbours.
Warren County, Cities and towns
Cities and towns in Warren County
About 16,222 people live in Warren County by the Census Bureau's estimate for July 1, 2025, 615 fewer than in 2020 (−3.7%). That works out to 30 people per square mile of land. Monmouth alone is home to 8,599 of them, 53.0% of the total. Reported testing is thin here: 42 tests over 2017, or 2.6 for every 1,000 residents (2025 estimate), where Illinois as a whole comes to 10.9.
From Monmouth to Little York, CDC publishes no figure by town: each reads Warren County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Monmouth | 8,599 | −3.6% | 53.0% |
| Roseville | 843 | −4.1% | 5.2% |
| Alexisextends beyond Warren County | 755 | −3.6% | Counted whole |
| Avonextends beyond Warren County | 672 | −4.1% | Counted whole |
| Kirkwood | 650 | −4.0% | 4.0% |
| Little York | 267 | −5.0% | 1.6% |
6 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 Warren County is counted whole, so it has no share.
Warren County, Homes
Homes in Warren County
Warren County is a place of houses on their own lots: 87% of its 7,598 homes are detached single-family houses, against 58% across Illinois. The homes are older than Illinois' as a whole: half were built before 1956 (1970 for Illinois), and 55% date from before 1960. Owners live in 78% of the occupied homes (Illinois: 67%), so for most households a test and a fix are their own to order.
| Homes | Warren County | Illinois |
|---|---|---|
| Housing units | 7,598 | 5,443,501 |
| Detached houses | 87% | 58% |
| In buildings of 5 or more | 7% | 22% |
| Mobile homes | 2% | 2% |
| Built before 1960 | 55% | 38% |
| Built since 2000 | 7% | 16% |
| Middle year built | 1956 | 1970 |
| Owner-occupied | 78% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.