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Radon Levels in Washington County, Kansas

EPA puts Washington County in Zone 1, its highest radon zone, and only 16 radon tests from it are on file with CDC (2022). 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

    55.0%

    23.2 pts above KS

    Washington
    55.0%
    Kansas
    31.8%

    60 tests, 2021

  • Median result

    5.3pCi/L

    Action level reached

    Washington
    5.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2021

  • Tests reported

    60

    44th of 62 by tests

    Washington
    60
    Johnson
    25,860

    Reported to CDC before any fix, 2021

  • 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 Kansas

    15 of 62

    Top quarter

    Washington
    55.0%
    Norton
    93.8%

    By share, of 62 with 30+ tests

Read a result for Washington County

Starts at Washington County's median, 5.3 pCi/L

5.3pCi/L

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

EPA’s reading of 5.3 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. Washington County's median reported result, 2021.

Interpret this readingWhat a fix costs

The data

Washington County, At a glance

Washington County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Washington 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 83% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Washington County, 2022

Share of reported tests at or above 4 pCi/L, by year, Washington County
Share of reported tests at or above 4 pCi/L, by year, Washington County
YearShare of reported tests at or above 4 pCi/L
201678.1%
201762.5%
201861.8%
201960.0%
202040.0%
202155.0%
202243.8%

2022: 43.8%. Across these years the share ran from 40.0% to 78.1%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

Only 16 tests were reported to CDC for Washington County over 2022, and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor this house.

Measured: CDC tracking data. Figure above: 2022. Measured data period: 2016 to 2022 (every CDC figure on file).

How to read these figures

Washington County, Compared

Washington County radon figures, compared

Calculated by Radon411

More than half: 55.0% of the 60 radon tests reported to CDC for Washington County in 2021 read at least 4 pCi/L. That places it 15th of 62 Kansas counties with 30 or more tests for the same period. That is 23.2 points above the 31.8% pooled from 96 Kansas counties.

The newest figure, in 2022, counts only 16 tests (43.8% at or above 4 pCi/L), too few to compare, so this reading uses the 60-test figure.

The median result, 5.3 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 24.5 pCi/L. The rest split 20.0% under 2 pCi/L and 25.0% from 2 to 4 (Kansas: 45.3% and 22.9%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 55.0% share point the same way here.

6 of its 8 bordering counties with figures ran higher, led by Thayer County, NE at 64.5%; Riley County reported 33.9%. Statewide for the same period, Norton County reported the highest share (93.8%) and Doniphan County the lowest (0.0%).

The busiest year on file was 2021, with 60 tests reported; the quietest, 2020, had 15.

Over 3 years of annual figures the share fell 23.1 points, from 78.1% in 2016 to 55.0% in 2021; its peak was 78.1% in 2016. Nationally, every county with a figure for the same period pools to 24.4%; Washington County sits 30.6 points above it. CDC also counts 15 tests taken after mitigation in Washington County for the same period: tests in homes where a fix was already in.

Share of reported tests at or above 4 pCi/L by year, Washington County against Kansas2016 to 2021, years with 30 or more tests: Washington County 78.1% to 55.0%, the state's pooled share 31.8% in 2021.
Washington CountyKansas, pooled
Share of reported tests at or above 4 pCi/L by year, Washington County against Kansas: data table
YearTestsWashington County, at or above 4 pCi/LKansas, pooled
20163278.1%35.4%
20185561.8%37.3%
20216055.0%31.8%
Washington County against Kansas, the United States and nearby counties, 2021
AreaTestsAt or above 4 pCi/LMedianDifference from Washington County
Washington County6055.0%5.3 pCi/LThis county
Kansas, pooled96 counties, pooled69,90931.8%Not pooled−23.2 points
United States, pooled807 counties, pooled344,60424.4%Not pooled−30.6 points
Norton Countyhighest in the state4893.8%7.3 pCi/L+38.8 points
Doniphan Countylowest in the state330.0%1.7 pCi/L−55.0 points
Thayer County, NEborders it9364.5%6.8 pCi/L+9.5 points
Marshall County, KSborders it9963.6%5.3 pCi/L+8.6 points
Gage County, NEborders it41763.3%5.5 pCi/L+8.3 points
Cloud County, KSborders it26460.2%4.4 pCi/L+5.2 points
Republic County, KSborders it4257.1%5.2 pCi/L+2.1 points
Jefferson County, NEborders it4856.3%4.7 pCi/L+1.3 points
Clay County, KSborders it37854.0%4.5 pCi/L−1.0 points
Riley County, KSborders it3,13233.9%2.3 pCi/L−21.1 points
Where Washington County's reported results fell, 2021, beside Kansas and the United States
ResultWashington County testsWashington County shareKansas shareU.S. shareAgainst Kansas
Under 2 pCi/L1220.0%45.3%54.4%−25.3 points
2 to 4 pCi/L1525.0%22.9%21.2%+2.1 points
4 pCi/L and above3355.0%31.8%24.4%+23.2 points
Washington County ranked among the 62 Kansas counties with 30 or more tests, by share at or above 4 pCi/L, 2021
CountyRankTestsAt or above 4 pCi/LMedian
Pawnee County10 of 629656.3%4.3 pCi/L
Russell County10 of 624856.3%4.8 pCi/L
Thomas County10 of 624856.3%4.2 pCi/L
Mitchell County13 of 6217755.9%4.8 pCi/L
Logan County14 of 6210255.9%4.6 pCi/L
Washington County15 of 626055.0%5.3 pCi/L
Clay County16 of 6237854.0%4.5 pCi/L
Nemaha County17 of 623953.8%4.8 pCi/L
Anderson County18 of 624553.3%4.2 pCi/L
Rice County19 of 626650.0%3.8 pCi/L
Rooks County19 of 626650.0%3.8 pCi/L
Washington County radon tests by year, against Kansas' pooled share
YearTestsAt or above 4 pCi/LMedianHighestKansas, pooledChange from the row before
20221643.8%3.3 pCi/L22.5 pCi/L32.0%−11.2 points
20216055.0%5.3 pCi/L24.5 pCi/L31.8%+15.0 points
20201540.0%2.5 pCi/L34.1 pCi/L31.3%−20.0 points
20192060.0%5.8 pCi/L19.1 pCi/L33.7%−1.8 points
20185561.8%6.0 pCi/L17.0 pCi/L37.3%−0.7 points
20172462.5%6.3 pCi/L17.8 pCi/L37.3%−15.6 points
20163278.1%8.3 pCi/L27.5 pCi/L35.4%First on file

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

Washington County, Geology

The ground under Washington County

Predicted

Most of the ground under Washington County is one class on USGS's geologic map: 82.7% of its land is high radon potential, with 17.3% moderate. The map puts 73.1% of Washington County in the area it calls Smoky Hills and 17.3% in Glaciated Area, with 2 smaller areas beside them. USGS gives the first a radon index of 12, in the high band (12 to 17), and the second 9, in the moderate band (9 to 11).

USGS's geologic areas under Washington County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Smoky HillsCretaceous marine sandstone, shale, and siltstone covered by discontinuous loess deposits.High1273.1%
Glaciated AreaGlacial till underlain by Pennsylvanian and Permian marine and nonmarine sedimentary shale, sandstone, limestone, coal.Moderate917.3%
Mid-Continent Rift ZoneFaulted and fractured Permian limestone, dolomite, shale, and sandstone related to the Mid-Continent Rift zone.High127.8%
Glacial DriftGlacial drift and loess of varying thickness, largely locally derived from underlying and nearby Paleozoic sedimentary rocks.High121.8%

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

Washington County beside the ground around it

Washington County has more high-potential ground than Kansas as a whole: 82.7% of its land against 59.9%. Of the 8 counties that border it, 7 have more high-potential ground, Cloud County the most at 100%.

Share of land by USGS radon potential: Washington County, the 8 counties bordering it and Kansas
AreaEPA zoneLow potentialModerate potentialHigh potential
Washington CountyZone 1None17.3%82.7%
Jefferson County, NEZone 1NoneNone100%
Clay CountyZone 1None34.7%65.3%
Republic CountyZone 1NoneNone100%
Marshall CountyZone 1None0.4%99.6%
Thayer County, NEZone 1NoneNone100%
Riley CountyZone 1NoneNone100%
Gage County, NEZone 1NoneNone100%
Cloud CountyZone 1NoneNone100%
Kansas105 counties, pooled by land areaVariesNone40.1%59.9%

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

Local help

Washington County, Local resources

Radon testing and mitigation in Washington County

What Kansas's program says
Phone
(800) 693-5343

What it means

Washington County, Questions

Questions about radon in Washington County

Are radon levels high in Washington County?

In 2022, 43.8% of the radon tests reported to CDC for Washington County, Kansas were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.3 pCi/L. Of 62 Kansas counties with 30 or more tests for the same period, 14 reported a higher share; pooled, the state comes to 31.8%.

Which counties border Washington County?

Washington County borders 8 counties: Jefferson County, NE, Clay County, KS, Republic County, KS, Marshall County, KS, Thayer County, NE, Riley County, KS, Gage County, NE and Cloud County, KS.

Products

Washington County, Products

Testing a home in Washington County

In Washington County, 55.0% of 60 tests reported to CDC in 2021 reached 4 pCi/L, against 31.8% pooled across Kansas. In Zone 1 the year-round level in Washington 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

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

Explore

Washington County, Bordering counties

Counties bordering Washington County

Calculated by Radon411

Washington County, Cities and towns

Cities and towns in Washington County

Washington County's population has barely moved since 2020: 5,533 residents on July 1, 2025 against 5,544 then, by the Census Bureau's estimates. Spread over its land, that is 6.2 people to the square mile. No town dominates: Washington, the largest, has 1,063 residents, 19.2% of the total. Reported testing is thin here: 60 tests over 2021, or 10.8 for every 1,000 residents (2025 estimate), where Kansas as a whole comes to 23.5.

From Washington to Hollenberg, CDC publishes no figure by town: each reads Washington County's.

The cities and towns in Washington County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Washington1,063−0.5%19.2%
Hanover690−0.7%12.5%
Cliftonextends beyond Washington County457+1.1%Counted whole
Linn386−0.3%7.0%
Greenleaf354−0.3%6.4%
Barnes162−0.6%2.9%
Palmer126−0.8%2.3%
Morrowville113−0.9%2.0%
Haddam108−0.9%2.0%
Mahaska43−2.3%0.8%
Viningextends beyond Washington County43+2.4%Counted whole
Hollenberg13Level0.2%

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

Washington County, Homes

Homes in Washington County

Washington County is a place of houses on their own lots: 90% of its 2,731 homes are detached single-family houses, against 72% across Kansas. The homes are older than Kansas' as a whole: half were built before 1954 (1975 for Kansas), and 57% date from before 1960. Owners live in 78% of the occupied homes (Kansas: 67%), so for most households a test and a fix are their own to order.

Homes in Washington County, Kansas, 2019 to 2023
HomesWashington CountyKansas
Housing units2,7311,285,221
Detached houses90%72%
In buildings of 5 or more1%13%
Mobile homes3%4%
Built before 196057%33%
Built since 200010%20%
Middle year built19541975
Owner-occupied78%67%

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