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 Mercer County, Illinois
EPA puts Mercer County in Zone 1, its highest radon zone, and high results are common there: 68.2% of the 66 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
68.2%
34.5 pts above IL
- Mercer
- 68.2%
- Illinois
- 33.7%
66 tests, 2017
Median result
5.5pCi/L
Action level reached
- Mercer
- 5.5 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2017
Tests reported
66
56th of 70 by tests
- Mercer
- 66
- 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
2 of 70
Top quarter
- Mercer
- 68.2%
- Stark
- 69.2%
By share, of 70 with 30+ tests
Read a result for Mercer County
Starts at Mercer County's median, 5.5 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 5.5 pCi/L
At or above 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Mercer County's median reported result, 2017.
The data
Mercer County, At a glance
Mercer County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Mercer 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 Mercer County, 2017
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 61.1% |
| 2015 | 65.0% |
| 2017 | 68.2% |
2017: 68.2%. Across these years the share ran from 61.1% to 68.2%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 66 tests reported to CDC for Mercer 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).
Mercer County, Compared
Mercer County radon figures, compared
Calculated by Radon411More than half: 68.2% of the 66 radon tests reported to CDC for Mercer County in 2017 read at least 4 pCi/L. That places it 2nd of 70 Illinois counties with 30 or more tests for the same period. That is 34.5 points above the 33.7% pooled from 93 Illinois counties.
The median result, 5.5 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 15.5 pCi/L. The rest split 18.2% under 2 pCi/L and 13.6% from 2 to 4 (Illinois: 37.7% and 28.6%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 68.2% share point the same way here.
No bordering county with a figure for the same period reported a higher share; the closest is Knox County at 56.6%, the lowest Rock Island County at 46.5%. 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 216 tests reported; the quietest, 2015, had 60.
Over 3 years of annual figures the share rose 7.1 points, from 61.1% in 2014 to 68.2% in 2017; its peak was 68.2% in 2017. Nationally, every county with a figure for the same period pools to 31.7%; Mercer County sits 36.5 points above it.
Mercer CountyIllinois, pooled
68.2% % of tests33.7% % of tests
| Year | Tests | Mercer County, at or above 4 pCi/L | Illinois, pooled |
|---|---|---|---|
| 2014 | 216 | 61.1% | 37.8% |
| 2015 | 60 | 65.0% | 36.6% |
| 2017 | 66 | 68.2% | 33.7% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Mercer County, Geology
The ground under Mercer County
PredictedUSGS's geologic map puts all of Mercer 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.
Mercer County beside the ground around it
Mercer County has more high-potential ground than Illinois as a whole: 100% of its land against 64.5%. Of the 8 counties that border it, none has as large a share of high-potential ground; Des Moines County, IA comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Mercer County, Local resources
Radon testing and mitigation in Mercer 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
Mercer County, Questions
Questions about radon in Mercer County
Are radon levels high in Mercer County?
In 2017, 68.2% of the radon tests reported to CDC for Mercer County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 5.5 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 1 reported a higher share; pooled, the state comes to 33.7%.
Which counties border Mercer County?
Mercer County borders 8 counties: Warren County, IL, Henderson County, IL, Muscatine County, IA, Louisa County, IA, Des Moines County, IA, Rock Island County, IL, Henry County, IL and Knox County, IL.
Products
Mercer County, Products
Testing a home in Mercer County
In Mercer County, 68.2% of 66 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 1 the year-round level in Mercer 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-1011S rechargeable radon detector with a screen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Semiconductor sensor
First reading: Within 12 hours
Short-term kit
PicoCan short-term charcoal canister radon test
- Lab fee included
Method: Charcoal
In home: 48 to 96 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Mercer County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Mercer County
Explore
Mercer County, Bordering counties
Counties bordering Mercer County
Calculated by Radon411- Radon levels in Knox County, ILEPA zone 1
56.6%at or above 4 pCi/L
Median 4.7 pCi/L · 249 tests · 11.6 points below Mercer County
- Radon levels in Henry County, ILEPA zone 1
55.7%at or above 4 pCi/L
Median 4.6 pCi/L · 420 tests · 12.5 points below Mercer County
- Radon levels in Warren County, ILEPA zone 1
50.0%at or above 4 pCi/L
Median 3.6 pCi/L · 42 tests · 18.2 points below Mercer County
- Radon levels in Rock Island County, ILEPA zone 1
46.5%at or above 4 pCi/L
Median 3.7 pCi/L · 2,283 tests · 21.7 points below Mercer County
- Radon levels in Henderson County, ILEPA zone 1
No CDC figure for 2017; its page reads it against its own neighbours.
- Radon levels in Muscatine County, IAEPA zone 1
No CDC figure for 2017; its page reads it against its own neighbours.
- Radon levels in Louisa County, IAEPA zone 1
No CDC figure for 2017; its page reads it against its own neighbours.
- Radon levels in Des Moines County, IAEPA zone 1
No CDC figure for 2017; its page reads it against its own neighbours.
Mercer County, Cities and towns
Cities and towns in Mercer County
About 15,229 people live in Mercer County by the Census Bureau's estimate for July 1, 2025, 408 fewer than in 2020 (−2.6%). That works out to 27 people per square mile of land. Its largest town, Aledo, has 3,506 residents, 23.0% of the total. Reported testing is thin here: 66 tests over 2017, or 4.3 for every 1,000 residents (2025 estimate), where Illinois as a whole comes to 10.9.
From Aledo to North Henderson, CDC publishes no figure by town: each reads Mercer County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Aledo | 3,506 | −3.1% | 23.0% |
| Viola | 836 | −3.6% | 5.5% |
| Alexisextends beyond Mercer County | 755 | −3.6% | Counted whole |
| Sherrard | 691 | Level | 4.5% |
| Matherville | 689 | −2.7% | 4.5% |
| Windsor | 649 | −3.1% | 4.3% |
| New Boston | 600 | −2.1% | 3.9% |
| Keithsburg | 546 | +0.2% | 3.6% |
| Reynoldsextends beyond Mercer County | 495 | −2.6% | Counted whole |
| Joy | 357 | −3.3% | 2.3% |
| Seaton | 208 | −3.7% | 1.4% |
| North Henderson | 159 | −2.5% | 1.0% |
12 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 Mercer County is counted whole, so it has no share.
Mercer County, Homes
Homes in Mercer County
Mercer County is a place of houses on their own lots: 88% of its 7,279 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. Owners live in 83% of the occupied homes (Illinois: 67%), so for most households a test and a fix are their own to order.
| Homes | Mercer County | Illinois |
|---|---|---|
| Housing units | 7,279 | 5,443,501 |
| Detached houses | 88% | 58% |
| In buildings of 5 or more | 4% | 22% |
| Mobile homes | 3% | 2% |
| Built before 1960 | 50% | 38% |
| Built since 2000 | 10% | 16% |
| Middle year built | 1960 | 1970 |
| Owner-occupied | 83% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.