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Radon Levels in LaSalle County, Illinois

EPA puts LaSalle County in Zone 1, its highest radon zone, and high results are common there: 45.8% of the 1,002 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

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    45.8%

    12.1 pts above IL

    LaSalle
    45.8%
    Illinois
    33.7%

    1,002 tests, 2017

  • Median result

    3.6pCi/L

    Below action level

    LaSalle
    3.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2017

  • Tests reported

    1,002

    19th of 70 by tests

    LaSalle
    1,002
    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

    31 of 70

    Middle half

    LaSalle
    45.8%
    Stark
    69.2%

    By share, of 70 with 30+ tests

Read a result for LaSalle County

Starts at LaSalle County's median, 3.6 pCi/L

3.6pCi/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

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

Interpret this readingWhat a fix costs

The data

LaSalle County, At a glance

LaSalle County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of LaSalle 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 LaSalle County, 2017

Share of reported tests at or above 4 pCi/L, by year, LaSalle County
Share of reported tests at or above 4 pCi/L, by year, LaSalle County
YearShare of reported tests at or above 4 pCi/L
201457.0%
201555.6%
201641.7%
201745.8%

2017: 45.8%. Across these years the share ran from 41.7% to 57.0%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 1,002 tests reported to CDC for LaSalle 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

LaSalle County, Compared

LaSalle County radon figures, compared

Calculated by Radon411

In LaSalle County, about 5 in 10 reported tests in 2017 (459 of 1,002) were at or above EPA's action level. Against the national pool of 31.7%, the gap is 14.1 points higher. Across 93 Illinois counties pooled together, 33.7% of tests reached that level, so LaSalle County runs 12.1 points above its state.

Of 9 neighbours with a figure, 5 reported a larger share at or above 4 pCi/L and 4 a smaller one; the spread is 32.3% (Grundy County) to 61.7% (Livingston County). By share, LaSalle County is 31st of 70 Illinois counties with 30 or more tests for the same period.

Year by year, 2014 opened at 57.0% and 2017 closed at 45.8% (down 11.2 points), with 2014 the high at 57.0%. Half the tests came in under 3.6 pCi/L and half over it; the single highest reached 75.2 pCi/L. Below the action level, 276 tests (27.5%) came in under 2 pCi/L, against 37.7% statewide, and 267 tests (26.6%) fell between 2 and 4, against 28.6% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 45.8% 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 1,011 tests reported; the quietest, 2016, had 36.

Share of reported tests at or above 4 pCi/L by year, LaSalle County against Illinois2014 to 2017, years with 30 or more tests: LaSalle County 57.0% to 45.8%, the state's pooled share 33.7% in 2017.
LaSalle CountyIllinois, pooled
Share of reported tests at or above 4 pCi/L by year, LaSalle County against Illinois: data table
YearTestsLaSalle County, at or above 4 pCi/LIllinois, pooled
20141,01157.0%37.8%
201539955.6%36.6%
20163641.7%17.4%
20171,00245.8%33.7%
LaSalle County against Illinois, the United States and nearby counties, 2017
AreaTestsAt or above 4 pCi/LMedianDifference from LaSalle County
LaSalle County1,00245.8%3.6 pCi/LThis county
Illinois, pooled93 counties, pooled138,00633.7%Not pooled−12.1 points
United States, pooled937 counties, pooled528,06231.7%Not pooled−14.1 points
Stark Countyhighest in the state3969.2%5.8 pCi/L+23.4 points
Williamson Countylowest in the state2498.4%0.9 pCi/L−37.4 points
Livingston County, ILborders it34561.7%5.3 pCi/L+15.9 points
Bureau County, ILborders it33358.6%5.1 pCi/L+12.8 points
Putnam County, ILborders it4553.3%4.5 pCi/L+7.5 points
Woodford County, ILborders it76552.9%4.2 pCi/L+7.1 points
Marshall County, ILborders it8148.1%3.8 pCi/L+2.3 points
Lee County, ILborders it21943.8%3.3 pCi/L−2.0 points
DeKalb County, ILborders it1,70741.1%3.3 pCi/L−4.7 points
Kendall County, ILborders it3,04535.0%2.8 pCi/L−10.8 points
Grundy County, ILborders it39032.3%2.4 pCi/L−13.5 points
Where LaSalle County's reported results fell, 2017, beside Illinois and the United States
ResultLaSalle County testsLaSalle County shareIllinois shareU.S. shareAgainst Illinois
Under 2 pCi/L27627.5%37.7%43.5%−10.2 points
2 to 4 pCi/L26726.6%28.6%24.8%−2.0 points
4 pCi/L and above45945.8%33.7%31.7%+12.1 points
LaSalle 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
Rock Island County26 of 702,28346.5%3.7 pCi/L
Jersey County27 of 7012946.5%3.6 pCi/L
Tazewell County28 of 702,72446.4%3.6 pCi/L
Adams County29 of 7088546.1%3.6 pCi/L
Logan County30 of 707245.8%3.4 pCi/L
LaSalle County31 of 701,00245.8%3.6 pCi/L
Jo Daviess County32 of 7051345.0%3.5 pCi/L
Champaign County33 of 703,15944.7%3.4 pCi/L
Montgomery County34 of 7012343.9%3.3 pCi/L
Lee County35 of 7021943.8%3.3 pCi/L
Sangamon County36 of 703,37843.7%3.7 pCi/L
LaSalle County radon tests by year, against Illinois' pooled share
YearTestsAt or above 4 pCi/LMedianHighestIllinois, pooledChange from the row before
20171,00245.8%3.6 pCi/L75.2 pCi/L33.7%+4.1 points
20163641.7%3.2 pCi/L14.5 pCi/L17.4%−13.9 points
201539955.6%4.4 pCi/L39.9 pCi/L36.6%−1.4 points
20141,01157.0%4.7 pCi/L1305.0 pCi/L37.8%First on file

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

LaSalle County, Geology

The ground under LaSalle County

Predicted

USGS's geologic map puts all of LaSalle 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 LaSalle 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.

LaSalle County beside the ground around it

LaSalle County has more high-potential ground than Illinois as a whole: 100% of its land against 64.5%. Of the 9 counties that border it, none has as large a share of high-potential ground; DeKalb County comes nearest at 100%.

Share of land by USGS radon potential: LaSalle County, the 9 counties bordering it and Illinois
AreaEPA zoneLow potentialModerate potentialHigh potential
LaSalle CountyZone 1NoneNone100%
Putnam CountyZone 1NoneNone100%
Grundy CountyZone 1NoneNone100%
Marshall CountyZone 1NoneNone100%
Livingston CountyZone 1NoneNone100%
Kendall CountyZone 1NoneNone100%
Woodford CountyZone 1NoneNone100%
Bureau CountyZone 1NoneNone100%
DeKalb CountyZone 1NoneNone100%
Lee 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

LaSalle County, Local resources

Radon testing and mitigation in LaSalle County

Listed radon businesses with an address in LaSalle County:

Listed radon professionals by town: Ottawa, Marseilles, Seneca, Leland

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

LaSalle County, Questions

Questions about radon in LaSalle County

Are radon levels high in LaSalle County?

In 2017, 45.8% of the radon tests reported to CDC for LaSalle 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, 30 reported a higher share; pooled, the state comes to 33.7%.

Which counties border LaSalle County?

LaSalle County borders 9 counties: Putnam County, Grundy County, Marshall County, Livingston County, Kendall County, Woodford County, Bureau County, DeKalb County and Lee County.

Products

LaSalle County, Products

Testing a home in LaSalle County

In LaSalle County, 45.8% of 1,002 tests reported to CDC in 2017 reached 4 pCi/L, against 33.7% pooled across Illinois. In Zone 1 the year-round level in LaSalle 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

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

Explore

LaSalle County, Bordering counties

Counties bordering LaSalle County

Calculated by Radon411

LaSalle County, Cities and towns

Cities and towns in LaSalle County

About 107,773 people live in LaSalle County by the Census Bureau's estimate for July 1, 2025, 1,638 fewer than in 2020 (−1.5%). That works out to 95 people per square mile of land. No town dominates: Ottawa, the largest, has 18,684 residents, 17.3% of the total. CDC's 1,002 reported tests for 2017 work out to 9.3 per 1,000 residents (2025 estimate), close to Illinois' 10.9.

From Ottawa to Leonore, CDC publishes no figure by town: each reads LaSalle County's.

The 12 largest cities and towns in LaSalle County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Ottawa18,684−0.6%17.3%
Streatorextends beyond LaSalle County12,190−2.2%Counted whole
Peruextends beyond LaSalle County9,780−1.4%Counted whole
LaSalle9,388−1.8%8.7%
Mendota6,894−2.1%6.4%
Marseilles4,809−1.3%4.5%
Oglesby3,618−2.1%3.4%
Senecaextends beyond LaSalle County2,310−1.6%Counted whole
Sheridan2,094−13.1%1.9%
Somonaukextends beyond LaSalle County1,770−1.2%Counted whole
Earlville1,590−1.4%1.5%
North Utica1,334+0.9%1.2%
  • Wenona (part)
  • Leland
  • Tonica
  • Dalzell (part)
  • Millington (part)
  • Grand Ridge
  • Lostant
  • Naplate
  • Ransom
  • Cedar Point
  • Rutland
  • Kangley
  • Troy Grove
  • Dana
  • Leonore

27 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. “(part)” marks a place that extends into another county. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond LaSalle County is counted whole, so it has no share.

LaSalle County, Homes

Homes in LaSalle County

LaSalle County is a place of houses on their own lots: 79% of its 49,838 homes are detached single-family houses, against 58% across Illinois. Half of its homes were built before 1963, close to Illinois' 1970: 47% date from before 1960 and 12% from 2000 or later. 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 in LaSalle County, Illinois, 2019 to 2023
HomesLaSalle CountyIllinois
Housing units49,8385,443,501
Detached houses79%58%
In buildings of 5 or more7%22%
Mobile homes4%2%
Built before 196047%38%
Built since 200012%16%
Middle year built19631970
Owner-occupied74%67%

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