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Radon Levels in Washtenaw County, Michigan

EPA puts Washtenaw County in Zone 1, its highest radon zone, and high results are common there: 41.3% of the 8,500 radon tests reported to CDC (2008 to 2017, laboratory totals) 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

    41.3%

    14.4 pts above MI

    Washtenaw
    41.3%
    Michigan
    26.9%

    8,500 tests, 2008 to 2017

  • Median result

    3.2pCi/L

    Below action level

    Washtenaw
    3.2 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    8,500

    2nd of 82 by tests

    Washtenaw
    8,500
    Oakland
    16,224

    Reported to CDC before any fix, 2008 to 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 Michigan

    6 of 82

    Top quarter

    Washtenaw
    41.3%
    Lenawee
    56.7%

    By share, of 82 with 30+ tests

Read a result for Washtenaw County

Starts at Washtenaw County's median, 3.2 pCi/L

3.2pCi/L

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

EPA’s reading of 3.2 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. Washtenaw County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Washtenaw County, At a glance

Washtenaw County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Washtenaw 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 85% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Washtenaw County, 2008 to 2017, laboratory

Reported results by concentration band, Washtenaw County, 2008 to 2017, laboratory
Under 2 pCi/L: 33%2 to 4 pCi/L: 26%4 pCi/L and above: 41%

Of 8,500 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Washtenaw County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L2,78332.7%
2 to 4 pCi/L2,21026.0%
4 pCi/L and above3,50741.3%
What these figures count

These are the 8,500 tests reported to CDC for Washtenaw County over 2008 to 2017 (laboratory totals), 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: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).

How to read these figures

Washtenaw County, Compared

Washtenaw County radon figures, compared

Calculated by Radon411

In Washtenaw County, about 4 in 10 reported tests over the 2008 to 2017 laboratory totals (3,507 of 8,500) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 5.6 points higher. Across 83 Michigan counties pooled together, 26.9% of tests reached that level, so Washtenaw County runs 14.4 points above its state.

Of 6 neighbours with a figure, 3 reported a larger share at or above 4 pCi/L and 3 a smaller one; the spread is 17.5% (Wayne County) to 56.7% (Lenawee County). By share, Washtenaw County is 6th of 82 Michigan counties with 30 or more tests for the same period.

Half the tests came in under 3.2 pCi/L and half over it; the single highest reached 328.5 pCi/L. Below the action level, 2,783 tests (32.7%) came in under 2 pCi/L, against 46.4% statewide, and 2,210 tests (26.0%) fell between 2 and 4, against 26.7% statewide.

Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 41.3% share point the same way here. USGS geology rates 85% of the county's land high radon potential. CDC also counts 1,099 tests taken after mitigation in Washtenaw County for the same period: tests in homes where a fix was already in.

CDC's ten-year totals for Washtenaw County went from 7,722 tests (2005 to 2014) to 8,500 (2008 to 2017), the share going from 42.1% to 41.3%.

Washtenaw County against Michigan, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Washtenaw County
Washtenaw County8,50041.3%3.2 pCi/LThis county
Michigan, pooled83 counties, pooled114,40726.9%Not pooled−14.4 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−5.6 points
Branch Countyhighest in the state1,04855.4%4.4 pCi/L+14.1 points
Muskegon Countylowest in the state6293.2%1.2 pCi/L−38.1 points
Lenawee County, MIborders it1,90756.7%4.6 pCi/L+15.4 points
Jackson County, MIborders it2,96449.7%3.9 pCi/L+8.4 points
Livingston County, MIborders it4,88543.1%3.4 pCi/L+1.8 points
Monroe County, MIborders it1,37530.4%2.5 pCi/L−10.9 points
Oakland County, MIborders it16,22428.8%2.3 pCi/L−12.5 points
Wayne County, MIborders it5,59417.5%1.8 pCi/L−23.8 points
Where Washtenaw County's reported results fell, 2008 to 2017, laboratory, beside Michigan and the United States
ResultWashtenaw County testsWashtenaw County shareMichigan shareU.S. shareAgainst Michigan
Under 2 pCi/L2,78332.7%46.4%39.6%−13.7 points
2 to 4 pCi/L2,21026.0%26.7%24.7%−0.7 points
4 pCi/L and above3,50741.3%26.9%35.7%+14.4 points
Washtenaw County ranked among the 82 Michigan counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Lenawee County1 of 821,90756.7%4.6 pCi/L
Branch County2 of 821,04855.4%4.4 pCi/L
Hillsdale County3 of 822,08654.8%4.4 pCi/L
Jackson County4 of 822,96449.7%3.9 pCi/L
Livingston County5 of 824,88543.1%3.4 pCi/L
Washtenaw County6 of 828,50041.3%3.2 pCi/L
Dickinson County7 of 8284339.3%3.1 pCi/L
Clinton County8 of 822,31338.5%3.1 pCi/L
Otsego County9 of 821,08038.2%3.2 pCi/L
Ionia County10 of 821,39136.8%2.9 pCi/L
Calhoun County11 of 821,64936.4%3.0 pCi/L
Washtenaw County ten-year laboratory totals, against Michigan's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMichigan, pooledChange from the row before
2008 to 20178,50041.3%3.2 pCi/L328.5 pCi/L26.9%−0.7 points
2007 to 20167,84142.0%3.2 pCi/L328.5 pCi/L26.8%−0.3 points
2006 to 20158,01142.3%3.3 pCi/L328.5 pCi/L26.8%+0.2 points
2005 to 20147,72242.1%3.2 pCi/L328.5 pCi/L26.2%First on file

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

Washtenaw County, State data

Michigan's own radon test data

Measured

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

MeasuredState figures, not CDC's

What Michigan EGLE reports for the ZIP codes in Washtenaw County

Michigan EGLE publishes its figures by ZIP code, not by county. These are the 25 ZIP codes that lie wholly or partly in Washtenaw County, each with the state's own figures for it. Period: About 10 years to 2026-05-15.

ZIP codes in Washtenaw County
ZIP codeWhat the state reports
4810337% greater than 4 pCi/L, median 2.9 pCi/L, 1,229 tests
4810434% greater than 4 pCi/L, median 2.7 pCi/L, 454 tests
4810538% greater than 4 pCi/L, median 2.9 pCi/L, 538 tests
4810825% greater than 4 pCi/L, median 1.9 pCi/L, 302 tests
4811119% greater than 4 pCi/L, median 1.8 pCi/L, 95 tests
4811848% greater than 4 pCi/L, median 3.8 pCi/L, 253 tests
4813049% greater than 4 pCi/L, median 3.8 pCi/L, 339 tests
4813750% greater than 4 pCi/L, median 4.0 pCi/L, 68 tests
4815862% greater than 4 pCi/L, median 5.5 pCi/L, 138 tests
4816032% greater than 4 pCi/L, median 2.7 pCi/L, 66 tests
4816739% greater than 4 pCi/L, median 3.1 pCi/L, 182 tests
4816829% greater than 4 pCi/L, median 2.2 pCi/L, 159 tests
4816945% greater than 4 pCi/L, median 3.4 pCi/L, 390 tests
4817023% greater than 4 pCi/L, median 2.3 pCi/L, 203 tests
4817643% greater than 4 pCi/L, median 3.2 pCi/L, 351 tests
4817831% greater than 4 pCi/L, median 2.4 pCi/L, 372 tests
4818951% greater than 4 pCi/L, median 4.0 pCi/L, 146 tests
481910% greater than 4 pCi/L, median 2.0 pCi/L, 13 tests
4819728% greater than 4 pCi/L, median 2.4 pCi/L, 473 tests
4819822% greater than 4 pCi/L, median 2.1 pCi/L, 202 tests
4922954% greater than 4 pCi/L, median 4.9 pCi/L, 35 tests
4923669% greater than 4 pCi/L, median 6.0 pCi/L, 54 tests
4924047% greater than 4 pCi/L, median 3.2 pCi/L, 59 tests
4928553% greater than 4 pCi/L, median 4.2 pCi/L, 17 tests
4928752% greater than 4 pCi/L, median 4.4 pCi/L, 27 tests
  • EGLE's figures cover first-time tests only, from organizations willing to provide data.
  • EGLE does not publish figures for a ZIP code with fewer than 5 test results.
  • EGLE says the map is not intended to decide whether a home should be tested: all homes should be tested.
  • ZIP code boundaries are postal delivery areas, not legal or administrative boundaries.
  • A ZIP code that crosses the county line is listed whole; its figures cover all of it.

Measured: Michigan EGLE data, About 10 years to 2026-05-15.

Washtenaw County, Geology

The ground under Washtenaw County

Predicted

Most of the ground under Washtenaw County is one class on USGS's geologic map: 84.9% of its land is high radon potential, with 15.1% moderate. The map puts 84.9% of Washtenaw County in the area it calls Saginaw Lobe Moraine Area and 15.1% in Antrim Shale-Lake deposits. 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 Washtenaw County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Saginaw Lobe Moraine AreaGlacial deposits derived from Sandstone and shale.High1284.9%
Antrim Shale-Lake depositsAntrim black shale covered by glacial lake deposits.Moderate915.1%

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

Washtenaw County beside the ground around it

Washtenaw County has more high-potential ground than Michigan as a whole: 84.9% of its land against 9.6%. Of the 6 counties that border it, 1 has more high-potential ground, Jackson County the most at 90.6%.

Share of land by USGS radon potential: Washtenaw County, the 6 counties bordering it and Michigan
AreaEPA zoneLow potentialModerate potentialHigh potential
Washtenaw CountyZone 1None15.1%84.9%
Lenawee CountyZone 1None31.4%68.6%
Monroe CountyZone 2None98.3%None
Wayne CountyZone 3None87.1%8.3%
Jackson CountyZone 1None9.4%90.6%
Livingston CountyZone 2None53.6%46.4%
Oakland CountyZone 2None56.8%43.2%
Michigan83 counties, pooled by land areaVaries45.0%44.3%9.6%

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

Local help

Washtenaw County, Local resources

Radon testing and mitigation in Washtenaw County

Listed radon businesses with an address in Washtenaw County:

Listed radon professionals by town: Ann Arbor

What Michigan's program says
Phone
800-723-6642
Email
Radon@Michigan.gov
Licensing of radon professionals
Michigan does not license or regulate radon testing and mitigation contractors.

What it means

Washtenaw County, Questions

Questions about radon in Washtenaw County

Are radon levels high in Washtenaw County?

Over the 2008 to 2017 laboratory totals, 41.3% of the radon tests reported to CDC for Washtenaw County, Michigan were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.2 pCi/L. Of 82 Michigan counties with 30 or more tests for the same period, 5 reported a higher share; pooled, the state comes to 26.9%.

Which counties border Washtenaw County?

Washtenaw County borders 6 counties: Lenawee County, Monroe County, Wayne County, Jackson County, Livingston County and Oakland County.

Products

Washtenaw County, Products

Testing a home in Washtenaw County

In Washtenaw County, 41.3% of 8,500 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 26.9% pooled across Michigan. In Zone 1 the year-round level in Washtenaw 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

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

Explore

Washtenaw County, Bordering counties

Counties bordering Washtenaw County

Calculated by Radon411

Washtenaw County, Cities and towns

Cities and towns in Washtenaw County

Washtenaw County's population has barely moved since 2020: 370,214 residents on July 1, 2025 against 371,814 then, by the Census Bureau's estimates. That works out to 524 people per square mile of land. Its largest town, Ann Arbor, has 122,233 residents, 33.0% of the total. Testing is reported here more often than across the state: CDC's 8,500 reported tests for 2008 to 2017 come to 23.0 for every 1,000 residents (2025 estimate), against 11.3 for Michigan.

From Ann Arbor to Barton Hills, CDC publishes no figure by town: each reads Washtenaw County's.

The cities and towns in Washtenaw County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Ann Arbor122,233−1.2%33.0%
Ypsilanti19,766−3.9%5.3%
Saline9,001+0.3%2.4%
Milanextends beyond Washtenaw County5,973−1.6%Counted whole
Chelsea5,424−0.4%1.5%
Dexter4,461−0.7%1.2%
Manchester2,027−2.6%0.5%
Barton Hills323−2.1%Under 0.1%

8 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 Washtenaw County is counted whole, so it has no share.

Washtenaw County, Homes

Homes in Washtenaw County

Of Washtenaw County's 158,115 homes, 57% are detached houses, against 72% across Michigan; 25% are in buildings of five or more homes. Half of its homes were built before 1978, close to Michigan's 1972: 25% date from before 1960 and 21% from 2000 or later. 62% of occupied homes are lived in by their owner (Michigan: 73%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Washtenaw County, Michigan, 2019 to 2023
HomesWashtenaw CountyMichigan
Housing units158,1154,599,683
Detached houses57%72%
In buildings of 5 or more25%13%
Mobile homes4%5%
Built before 196025%36%
Built since 200021%15%
Middle year built19781972
Owner-occupied62%73%

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