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 Carroll County, Illinois
EPA puts Carroll County in Zone 1, its highest radon zone, and high results are common there: 62.9% of the 210 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
62.9%
29.2 pts above IL
- Carroll
- 62.9%
- Illinois
- 33.7%
210 tests, 2017
Median result
5.5pCi/L
Action level reached
- Carroll
- 5.5 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2017
Tests reported
210
41st of 70 by tests
- Carroll
- 210
- 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
5 of 70
Top quarter
- Carroll
- 62.9%
- Stark
- 69.2%
By share, of 70 with 30+ tests
Read a result for Carroll County
Starts at Carroll 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. Carroll County's median reported result, 2017.
The data
Carroll County, At a glance
Carroll County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Carroll 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 Carroll County, 2017
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2014 | 73.6% |
| 2015 | 63.3% |
| 2016 | 100.0% |
| 2017 | 62.9% |
2017: 62.9%. Across these years the share ran from 62.9% to 100.0%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 210 tests reported to CDC for Carroll 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).
Carroll County, Compared
Carroll County radon figures, compared
Calculated by Radon411More than half: 62.9% of the 210 radon tests reported to CDC for Carroll County in 2017 read at least 4 pCi/L. That places it 5th of 70 Illinois counties with 30 or more tests for the same period. That is 29.2 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 59.2 pCi/L. The rest split 18.6% under 2 pCi/L and 18.6% from 2 to 4 (Illinois: 37.7% and 28.6%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 62.9% share point the same way here.
No bordering county with a figure for the same period reported a higher share; the closest is Stephenson County at 57.2%, the lowest Whiteside County at 43.1%. 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 318 tests reported; the quietest, 2016, had 3.
Over 3 years of annual figures the share fell 10.7 points, from 73.6% in 2014 to 62.9% in 2017; its peak was 73.6% in 2014. Nationally, every county with a figure for the same period pools to 31.7%; Carroll County sits 31.2 points above it.
Carroll CountyIllinois, pooled
62.9% % of tests33.7% % of tests
| Year | Tests | Carroll County, at or above 4 pCi/L | Illinois, pooled |
|---|---|---|---|
| 2014 | 318 | 73.6% | 37.8% |
| 2015 | 90 | 63.3% | 36.6% |
| 2017 | 210 | 62.9% | 33.7% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Carroll County, Geology
The ground under Carroll County
PredictedUSGS's geologic map puts all of Carroll County's mapped land in one class: high radon potential. The map puts 89.0% of Carroll County in the area it calls Galesburg Plain and 10.9% in Driftless Area. USGS gives the first a radon index of 13 and the second 12, both 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 | 89.0% |
| Driftless Area | Cambrian sandstone and Ordovician limestone and dolostone. | High | 12 | 10.9% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Carroll County beside the ground around it
Carroll 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; Jackson County, IA comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Carroll County, Local resources
Radon testing and mitigation in Carroll County
Listed radon businesses with an address in Carroll 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: Savanna
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
Carroll County, Questions
Questions about radon in Carroll County
Are radon levels high in Carroll County?
In 2017, 62.9% of the radon tests reported to CDC for Carroll 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, 4 reported a higher share; pooled, the state comes to 33.7%.
Which counties border Carroll County?
Carroll County borders 6 counties: Whiteside County, IL, Stephenson County, IL, Jo Daviess County, IL, Ogle County, IL, Clinton County, IA and Jackson County, IA.
Products
Carroll County, Products
Testing a home in Carroll County
In Carroll County, 62.9% of 210 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 1 the year-round level in Carroll 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-3786 rechargeable radon monitor with a 3.5-inch color screen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Ion chamber
First reading: Within 10 minutes
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
Carroll County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Carroll County
Explore
Carroll County, Bordering counties
Counties bordering Carroll County
Calculated by Radon411- Radon levels in Stephenson County, ILEPA zone 1
57.2%at or above 4 pCi/L
Median 4.8 pCi/L · 519 tests · 5.7 points below Carroll County
- Radon levels in Ogle County, ILEPA zone 1
52.4%at or above 4 pCi/L
Median 4.1 pCi/L · 636 tests · 10.5 points below Carroll County
- Radon levels in Jo Daviess County, ILEPA zone 1
45.0%at or above 4 pCi/L
Median 3.5 pCi/L · 513 tests · 17.9 points below Carroll County
- Radon levels in Whiteside County, ILEPA zone 1
43.1%at or above 4 pCi/L
Median 3.3 pCi/L · 696 tests · 19.8 points below Carroll County
- Radon levels in Clinton County, IAEPA zone 1
No CDC figure for 2017; its page reads it against its own neighbours.
- Radon levels in Jackson County, IAEPA zone 1
No CDC figure for 2017; its page reads it against its own neighbours.
Carroll County, Cities and towns
Cities and towns in Carroll County
About 15,419 people live in Carroll County by the Census Bureau's estimate for July 1, 2025, 267 fewer than in 2020 (−1.7%). That works out to 35 people per square mile of land. No town dominates: Savanna, the largest, has 2,699 residents, 17.5% of the total. Together its 7 incorporated places hold 61.5% of those residents; the other 38.5% live outside any of them. CDC's 210 reported tests for 2017 work out to 13.6 per 1,000 residents (2025 estimate), close to Illinois' 10.9.
From Savanna to Chadwick, CDC publishes no figure by town: each reads Carroll County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Savanna | 2,699 | −3.6% | 17.5% |
| Thomson | 1,606 | −0.4% | 10.4% |
| Lanark | 1,452 | −3.6% | 9.4% |
| Mount Carroll | 1,432 | −3.7% | 9.3% |
| Milledgeville | 988 | −3.6% | 6.4% |
| Shannon | 835 | +4.9% | 5.4% |
| Chadwick | 476 | −1.2% | 3.1% |
7 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).
Carroll County, Homes
Homes in Carroll County
Carroll County is a place of houses on their own lots: 86% of its 8,190 homes are detached single-family houses, against 58% across Illinois. The homes are older than Illinois' as a whole: half were built before 1959 (1970 for Illinois), and 52% 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 | Carroll County | Illinois |
|---|---|---|
| Housing units | 8,190 | 5,443,501 |
| Detached houses | 86% | 58% |
| In buildings of 5 or more | 6% | 22% |
| Mobile homes | 4% | 2% |
| Built before 1960 | 52% | 38% |
| Built since 2000 | 11% | 16% |
| Middle year built | 1959 | 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.