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Radon Levels in Piatt County, Illinois

EPA puts Piatt County in Zone 1, its highest radon zone, and high results are common there: 54.8% of the 279 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

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  • Share at 4+ pCi/L

    54.8%

    21.1 pts above IL

    Piatt
    54.8%
    Illinois
    33.7%

    279 tests, 2017

  • Median result

    4.3pCi/L

    Action level reached

    Piatt
    4.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2017

  • Tests reported

    279

    35th of 70 by tests

    Piatt
    279
    Cook
    26,937

    Reported to CDC before any fix, 2017

  • EPA radon zone

    Zone 1

    Highest potential

    1. Zone 1
    2. 2
    3. 3

    1 highest, 3 lowest

    EPA predicts over 4 pCi/L indoors

  • Rank in Illinois

    14 of 70

    Top quarter

    Piatt
    54.8%
    Stark
    69.2%

    By share, of 70 with 30+ tests

Read a result for Piatt County

Starts at Piatt County's median, 4.3 pCi/L

4.3pCi/L

EPA’s own thresholds; the figures are the area’s, never this home’s.

EPA’s reading of 4.3 pCi/L

At or above 4 pCi/L

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 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. Piatt County's median reported result, 2017.

Interpret this readingWhat a fix costs

The data

Piatt County, At a glance

Piatt County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Piatt County in and predicts an average indoor of greater than 4 pCi/L (greater than 150 Bq/m³) across the county. That is one forecast for the whole county, not a reading of any address in it; homes above EPA's turn up in all three zones.

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 Piatt County, 2017

Share of reported tests at or above 4 pCi/L, by year, Piatt County
Share of reported tests at or above 4 pCi/L, by year, Piatt County
YearShare of reported tests at or above 4 pCi/L
201456.0%
201564.3%
201754.8%

2017: 54.8%. Across these years the share ran from 54.8% to 64.3%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 279 tests reported to CDC for Piatt 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).

How to read these figures

Piatt County, Compared

Piatt County radon figures, compared

Calculated by Radon411

More than half: 54.8% of the 279 radon tests reported to CDC for Piatt County in 2017 read at least 4 pCi/L. That places it 14th of 70 Illinois counties with 30 or more tests for the same period. That is 21.1 points above the 33.7% pooled from 93 Illinois counties.

The median result, 4.3 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 29.8 pCi/L. The rest split 15.1% under 2 pCi/L and 30.1% from 2 to 4 (Illinois: 37.7% and 28.6%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 54.8% share point the same way here.

1 of its 6 bordering counties with figures ran higher, led by De Witt County at 57.1%; Macon County reported 38.8%. 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 300 tests reported; the quietest, 2015, had 126.

Over 3 years of annual figures the share held within 2 points, from 56.0% in 2014 to 54.8% in 2017; its peak was 64.3% in 2015. Nationally, every county with a figure for the same period pools to 31.7%; Piatt County sits 23.1 points above it.

Share of reported tests at or above 4 pCi/L by year, Piatt County against Illinois2014 to 2017, years with 30 or more tests: Piatt County 56.0% to 54.8%, the state's pooled share 33.7% in 2017.
Piatt CountyIllinois, pooled
Share of reported tests at or above 4 pCi/L by year, Piatt County against Illinois: data table
YearTestsPiatt County, at or above 4 pCi/LIllinois, pooled
201430056.0%37.8%
201512664.3%36.6%
201727954.8%33.7%
Piatt County against Illinois, the United States and nearby counties, 2017
AreaTestsAt or above 4 pCi/LMedianDifference from Piatt County
Piatt County27954.8%4.3 pCi/LThis county
Illinois, pooled93 counties, pooled138,00633.7%Not pooled−21.1 points
United States, pooled937 counties, pooled528,06231.7%Not pooled−23.1 points
Stark Countyhighest in the state3969.2%5.8 pCi/L+14.4 points
Williamson Countylowest in the state2498.4%0.9 pCi/L−46.4 points
De Witt County, ILborders it12657.1%5.2 pCi/L+2.3 points
Douglas County, ILborders it8450.0%3.8 pCi/L−4.8 points
Moultrie County, ILborders it4546.7%3.3 pCi/L−8.1 points
Champaign County, ILborders it3,15944.7%3.4 pCi/L−10.1 points
McLean County, ILborders it4,54842.5%3.3 pCi/L−12.3 points
Macon County, ILborders it1,25138.8%3.1 pCi/L−16.0 points
Where Piatt County's reported results fell, 2017, beside Illinois and the United States
ResultPiatt County testsPiatt County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L4215.1%37.7%43.5%−22.6 points
2 to 4 pCi/L8430.1%28.6%24.8%+1.5 points
4 pCi/L and above15354.8%33.7%31.7%+21.1 points
Piatt County ranked among the 70 Illinois counties with 30 or more tests, by share at or above 4 pCi/L, 2017
CountyRankTestsAt or above 4 pCi/LMedian
De Witt County9 of 7012657.1%5.2 pCi/L
Ford County9 of 704257.1%4.0 pCi/L
Knox County11 of 7024956.6%4.7 pCi/L
Henry County12 of 7042055.7%4.6 pCi/L
McDonough County12 of 7021055.7%4.3 pCi/L
Piatt County14 of 7027954.8%4.3 pCi/L
Vermilion County15 of 703953.8%4.7 pCi/L
Putnam County16 of 704553.3%4.5 pCi/L
Woodford County17 of 7076552.9%4.2 pCi/L
Ogle County18 of 7063652.4%4.1 pCi/L
Menard County19 of 7016851.8%4.3 pCi/L
Piatt County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
201727954.8%4.3 pCi/L29.8 pCi/L33.7%−9.5 points
201512664.3%5.3 pCi/L27.2 pCi/L36.6%+8.3 points
201430056.0%4.6 pCi/L31.5 pCi/L37.8%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period.

Piatt County, Geology

The ground under Piatt County

Predicted

USGS's geologic map puts all of Piatt County's mapped land in one class: high radon potential. All of it lies in the area the map calls Bloomington Ridged Plain, to which USGS gives a radon index of 13, in the high band (12 to 17).

USGS's geologic areas under Piatt County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Bloomington Ridged PlainWisconsinan glacial deposits and loess over Paleozoic sedimentary rocks.High13100%

Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.

Piatt County beside the ground around it

Piatt 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; Champaign County comes nearest at 100%.

Share of land by USGS radon potential: Piatt County, the 6 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
Piatt CountyZone 1NoneNone100%
Macon CountyZone 1NoneNone100%
Champaign CountyZone 1NoneNone100%
De Witt CountyZone 1NoneNone100%
Moultrie CountyZone 1NoneNone100%
Douglas CountyZone 1NoneNone100%
McLean CountyZone 1NoneNone100%
Illinois102 counties, pooled by land areaVaries0.9%34.5%64.5%

The map rates the ground, not the air in any home.

Local help

Piatt County, Local resources

Radon testing and mitigation in Piatt County

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

Piatt County, Questions

Questions about radon in Piatt County

Are radon levels high in Piatt County?

In 2017, 54.8% of the radon tests reported to CDC for Piatt County, Illinois were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.3 pCi/L. Of 70 Illinois counties with 30 or more tests for the same period, 13 reported a higher share; pooled, the state comes to 33.7%.

Which counties border Piatt County?

Piatt County borders 6 counties: Macon County, Champaign County, De Witt County, Moultrie County, Douglas County and McLean County.

Products

Piatt County, Products

Testing a home in Piatt County

In Piatt County, 54.8% of 279 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 1 the year-round level in Piatt 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

Piatt County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Piatt County

Explore

Piatt County, Bordering counties

Counties bordering Piatt County

Calculated by Radon411

Piatt County, Cities and towns

Cities and towns in Piatt County

The Census Bureau estimates 16,791 residents in Piatt County for July 1, 2025, 103 more than in 2020 (+0.6%). That works out to 38 people per square mile of land. Its largest town, Monticello, has 6,080 residents, 36.2% of the total. Testing is reported here more often than across the state: CDC's 279 reported tests for 2017 come to 16.6 for every 1,000 residents (2025 estimate), against 10.9 for Illinois.

From Monticello to Cisco, CDC publishes no figure by town: each reads Piatt County's.

The cities and towns in Piatt County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Monticello6,080+2.2%36.2%
Bement1,462−1.3%8.7%
Cerro Gordo1,312−0.9%7.8%
Atwoodextends beyond Piatt County1,100−0.9%Counted whole
Mansfield921−1.2%5.5%
Hammond499−1.2%3.0%
De Land447−1.3%2.7%
Ivesdaleextends beyond Piatt County255−3.0%Counted whole
Cisco254−1.6%1.5%

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 Piatt County is counted whole, so it has no share.

Piatt County, Homes

Homes in Piatt County

Piatt County is a place of houses on their own lots: 86% of its 7,380 homes are detached single-family houses, against 58% across Illinois. Half of its homes were built before 1972, close to Illinois' 1970: 35% date from before 1960 and 16% from 2000 or later. Owners live in 85% of the occupied homes (Illinois: 67%), so for most households a test and a fix are their own to order.

Homes in Piatt County, Illinois, 2019 to 2023
HomesPiatt CountyIllinois
Housing units7,3805,443,501
Detached houses86%58%
In buildings of 5 or more4%22%
Mobile homes2%2%
Built before 196035%38%
Built since 200016%16%
Middle year built19721970
Owner-occupied85%67%

Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.