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Radon Levels in Washington County, Minnesota

EPA puts Washington County in Zone 1, its highest radon zone, and 21.3% of its 1,518 reported radon tests (2023) were 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

    21.3%

    13.3 pts below MN

    Washington
    21.3%
    Minnesota
    34.6%

    1,518 tests, 2023

  • Median result

    1.9pCi/L

    Below action level

    Washington
    1.9 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2023

  • Tests reported

    1,518

    4th of 62 by tests

    Washington
    1,518
    Hennepin
    6,545

    Reported to CDC before any fix, 2023

  • 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 Minnesota

    58 of 62

    Lowest quarter

    Washington
    21.3%
    Renville
    75.7%

    By share, of 62 with 30+ tests

Read a result for Washington County

Starts at Washington County's median, 1.9 pCi/L

1.9pCi/L

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

EPA’s reading of 1.9 pCi/L

Below 2 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 below 2 pCi/L, the level at which EPA says a fix should be considered. Washington County's median reported result, 2023.

Interpret this reading

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 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Washington County, 2023

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
201433.1%
201533.4%
201628.1%
201730.4%
201831.6%
201929.0%
202026.3%
202125.5%
202226.5%
202321.3%

2023: 21.3%. Across these years the share ran from 21.3% to 33.4%. Each column counts radon tests reported to CDC that year, not homes.

What these figures count

These are the 1,518 tests reported to CDC for Washington County over 2023, 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: 2023. Measured data period: 2005 to 2023 (every CDC figure on file).

How to read these figures

Washington County, Compared

Washington County radon figures, compared

Calculated by Radon411

Washington County's 1,518 reported tests in 2023 had a middle value of 1.9 pCi/L and a maximum of 49.1 pCi/L, and 21.3% reached 4 pCi/L. Minnesota as a whole (86 Minnesota counties, pooled) comes to 34.6%: 13.3 points higher than here.

Among its state's counties it ranks 58th of 62 Minnesota counties with 30 or more tests for the same period. Statewide for the same period, Renville County reported the highest share (75.7%) and Lake County the lowest (3.8%).

Below the action level, 780 tests (51.4%) came in under 2 pCi/L, against 36.6% statewide, and 415 tests (27.3%) fell between 2 and 4, against 28.9% statewide. The busiest year on file was 2015, with 1,964 tests reported; the quietest, 2019, had 844.

EPA's 1993 zone map puts Washington County in Zone 1, a predicted county average above 4 pCi/L. USGS geology rates 100% of the county's land high radon potential.

Next door, the shares run from 19.3% in Anoka County to 37.4% in St. Croix County, WI, with Anoka County below Washington County. Over 10 years of annual figures the share fell 11.8 points, from 33.1% in 2014 to 21.3% in 2023; its peak was 33.4% in 2015.

Share of reported tests at or above 4 pCi/L by year, Washington County against Minnesota2014 to 2023, years with 30 or more tests: Washington County 33.1% to 21.3%, the state's pooled share 34.6% in 2023.
Washington CountyMinnesota, pooled
Share of reported tests at or above 4 pCi/L by year, Washington County against Minnesota: data table
YearTestsWashington County, at or above 4 pCi/LMinnesota, pooled
20141,81633.1%42.9%
20151,96433.4%43.6%
20161,84328.1%37.0%
20171,70330.4%38.2%
20181,84031.6%38.3%
201984429.0%36.1%
20201,28326.3%31.8%
20211,38525.5%33.1%
20221,27426.5%31.6%
20231,51821.3%34.6%
Washington County against Minnesota, the United States and nearby counties, 2023
AreaTestsAt or above 4 pCi/LMedianDifference from Washington County
Washington County1,51821.3%1.9 pCi/LThis county
Minnesota, pooled86 counties, pooled22,44934.6%Not pooled+13.3 points
United States, pooled642 counties, pooled128,74033.4%Not pooled+12.1 points
Renville Countyhighest in the state3775.7%6.3 pCi/L+54.4 points
Lake Countylowest in the state783.8%1.3 pCi/L−17.5 points
St. Croix County, WIborders it34837.4%3.0 pCi/L+16.1 points
Chisago County, MNborders it16634.9%2.9 pCi/L+13.6 points
Dakota County, MNborders it2,18334.6%2.9 pCi/L+13.3 points
Polk County, WIborders it12233.6%2.8 pCi/L+12.3 points
Pierce County, WIborders it13630.9%2.7 pCi/L+9.6 points
Ramsey County, MNborders it2,21323.5%2.2 pCi/L+2.2 points
Anoka County, MNborders it88019.3%1.9 pCi/L−2.0 points
Where Washington County's reported results fell, 2023, beside Minnesota and the United States
ResultWashington County testsWashington County shareMinnesota shareU.S. shareAgainst Minnesota
Under 2 pCi/L78051.4%36.6%41.4%+14.8 points
2 to 4 pCi/L41527.3%28.9%25.2%−1.6 points
4 pCi/L and above32321.3%34.6%33.4%−13.3 points
Washington County ranked among the 62 Minnesota counties with 30 or more tests, by share at or above 4 pCi/L, 2023
CountyRankTestsAt or above 4 pCi/LMedian
Cass County52 of 6210625.5%2.3 pCi/L
Todd County53 of 626323.8%2.0 pCi/L
Ramsey County54 of 622,21323.5%2.2 pCi/L
Benton County55 of 624323.3%2.2 pCi/L
Isanti County56 of 626622.7%2.0 pCi/L
Sherburne County57 of 6235121.7%1.8 pCi/L
Washington County58 of 621,51821.3%1.9 pCi/L
St. Louis County59 of 6249620.2%1.7 pCi/L
Anoka County60 of 6288019.3%1.9 pCi/L
Cook County61 of 623212.5%1.8 pCi/L
Lake County62 of 62783.8%1.3 pCi/L
Washington County radon tests by year, against Minnesota's pooled share
YearTestsAt or above 4 pCi/LMedianHighestMinnesota, pooledChange from the row before
20231,51821.3%1.9 pCi/L49.1 pCi/L34.6%−5.2 points
20221,27426.5%2.3 pCi/L33.0 pCi/L31.6%+1.0 points
20211,38525.5%2.4 pCi/L52.5 pCi/L33.1%−0.8 points
20201,28326.3%2.5 pCi/L29.7 pCi/L31.8%−2.7 points
201984429.0%2.7 pCi/L40.6 pCi/L36.1%−2.6 points
20181,84031.6%2.7 pCi/L413.0 pCi/L38.3%+1.2 points
20171,70330.4%2.7 pCi/L177.0 pCi/L38.2%+2.3 points
20161,84328.1%2.4 pCi/L71.0 pCi/L37.0%−5.3 points
20151,96433.4%2.7 pCi/L107.0 pCi/L43.6%+0.3 points
20141,81633.1%2.7 pCi/L60.0 pCi/L42.9%First on file

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

Washington County, State data

Minnesota's own radon test data

Measured

What Minnesota's own agencies publish about radon tests in Washington County, with their period. These are not CDC's figures and are never added to them.

MeasuredState figures, not CDC's

What the Minnesota Department of Health reports for Washington County

Radon Testing (MN Public Health Data Access Portal): home radon tests reported voluntarily by private laboratories and licensed radon measurement professionals, counted by property. Period: 2016-2025.

Share with one or more tests at or above 4 pCi/L

27.9%

4,235 properties tested with one or more tests at or above 4 pCi/L

Median result

2.4 pCi/L

Average result

3.2 pCi/L

Tests behind these figures

1,519 properties tested a year on average

  • MDH says these data do not include all of the radon tests conducted in Minnesota.
  • Post-mitigation tests are excluded from the averages and the median; the percentages use each property's highest test.
  • Each home is unique and can have very different results than a neighbor's home; the only way to know is to test.
  • These figures describe tests reported to the Minnesota Department of Health in this area. They count a different set of tests than CDC's figures and are not a reading of any one home.

Measured: Minnesota Department of Health data, 2016-2025.

Washington County, Geology

The ground under Washington County

Predicted

USGS's geologic map puts all of Washington County's mapped land in one class: high radon potential. The map puts 82.7% of Washington County in the area it calls Central Lowland-Western Lake Section and 17.2% in Central Lowland-Till Prairie. USGS gives both a radon index of 14, in the high band (12 to 17).

USGS's geologic areas under Washington County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Central Lowland-Western Lake SectionRed sandy till derived primarily from sandstone.High1482.7%
Central Lowland-Till PrairieSilty and clayey till derived from shale and sandstone.High1417.2%

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 Minnesota as a whole: 100% of its land against 61.1%. Of the 7 counties that border it, none has as large a share of high-potential ground; Anoka County comes nearest at 100%.

Share of land by USGS radon potential: Washington County, the 7 counties bordering it and Minnesota
AreaEPA zoneLow potentialModerate potentialHigh potential
Washington CountyZone 1NoneNone100%
Ramsey CountyZone 1NoneNone100%
St. Croix County, WIZone 1None0.3%99.7%
Dakota CountyZone 1NoneNone100%
Anoka CountyZone 2NoneNone100%
Pierce County, WIZone 1NoneNone100%
Chisago CountyZone 2NoneNone100%
Polk County, WIZone 2None86.6%13.4%
Minnesota87 counties, pooled by land areaVariesNone38.9%61.1%

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

Local help

Washington County, Local resources

Radon testing and mitigation in Washington County

Listed radon businesses with an address in Washington County:

Listed radon professionals by town: Woodbury, Cottage Grove, Oakdale, Hastings, Forest Lake, Stillwater

What Minnesota's program says
Phone
651-201-4601
Email
health.indoorair@state.mn.us
Licensing of radon professionals
The Radon Licensing Act requires anyone who performs a radon test or radon mitigation, in a building they do not own or lease, must be licensed by MDH.
Disclosure when a home is sold or rented
The Minnesota Radon Awareness Act requires specific disclosure and education be provided to potential home buyers during residential real estate transactions in Minnesota.

What it means

Washington County, Questions

Questions about radon in Washington County

Are radon levels high in Washington County?

In 2023, 21.3% of the radon tests reported to CDC for Washington County, Minnesota were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.9 pCi/L. Of 62 Minnesota counties with 30 or more tests for the same period, 57 reported a higher share; pooled, the state comes to 34.6%.

Which counties border Washington County?

Washington County borders 7 counties: Ramsey County, MN, St. Croix County, WI, Dakota County, MN, Anoka County, MN, Pierce County, WI, Chisago County, MN and Polk County, WI.

Products

Washington County, Products

Testing a home in Washington County

In Washington County, 21.3% of 1,518 tests reported to CDC in 2023 reached 4 pCi/L, against 34.6% pooled across Minnesota. 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 is growing: the Census Bureau puts it at 286,895 residents on July 1, 2025, up 6.9% from 268,397 in 2020. That works out to 746 people per square mile of land. Its largest town, Woodbury, has 81,558 residents, 28.4% of the total. CDC's 1,518 reported tests for 2023 work out to 5.3 per 1,000 residents (2025 estimate), close to Minnesota's 3.9.

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

The 12 largest cities and towns in Washington County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Woodbury81,558+8.1%28.4%
Cottage Grove43,604+11.8%15.2%
Oakdale30,588+8.2%10.7%
White Bear Lakeextends beyond Washington County23,392−5.6%Counted whole
Hastingsextends beyond Washington County22,563+1.8%Counted whole
Forest Lake20,952+1.2%7.3%
Stillwater19,354−0.2%6.7%
Hugo17,167+8.6%6.0%
Lake Elmo14,376+26.7%5.0%
Mahtomedi8,189+0.6%2.9%
Newport5,525+40.2%1.9%
St. Paul Park5,396−2.7%1.9%
  • Oak Park Heights
  • Scandia
  • Grant
  • Bayport
  • Afton
  • Lakeland
  • Dellwood
  • Lake St. Croix Beach
  • Landfall
  • Birchwood Village
  • Marine on St. Croix
  • Willernie
  • Pine Springs
  • St. Marys Point
  • Lakeland Shores

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

Washington County, Homes

Homes in Washington County

Of Washington County's 107,035 homes, 68% are detached houses, against 66% across Minnesota; 12% are in buildings of five or more homes. Much of Washington County is recent building: 32% of its homes have gone up since 2000 and the middle year built is 1992, against 1978 for Minnesota. Owners live in 81% of the occupied homes (Minnesota: 72%), so for most households a test and a fix are their own to order.

Homes in Washington County, Minnesota, 2019 to 2023
HomesWashington CountyMinnesota
Housing units107,0352,519,538
Detached houses68%66%
In buildings of 5 or more12%19%
Mobile homes2%3%
Built before 196013%29%
Built since 200032%22%
Middle year built19921978
Owner-occupied81%72%

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