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Radon Levels in Ontonagon County, Michigan

EPA puts Ontonagon County in Zone 3, its lowest radon zone, and most reported tests there come back low, though 11.4% of 123 (2008 to 2017, laboratory totals) reached 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

    11.4%

    15.5 pts below MI

    Ontonagon
    11.4%
    Michigan
    26.9%

    123 tests, 2008 to 2017

  • Median result

    1.3pCi/L

    Below action level

    Ontonagon
    1.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    123

    74th of 82 by tests

    Ontonagon
    123
    Oakland
    16,224

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 3

    Lower potential

    1. 1
    2. 2
    3. Zone 3

    1 highest, 3 lowest

    EPA predicts under 2 pCi/L indoors

  • Rank in Michigan

    65 of 82

    Lowest quarter

    Ontonagon
    11.4%
    Lenawee
    56.7%

    By share, of 82 with 30+ tests

Read a result for Ontonagon County

Starts at Ontonagon County's median, 1.3 pCi/L

1.3pCi/L

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

EPA’s reading of 1.3 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. Ontonagon County's median reported result, 2008 to 2017.

Interpret this reading

The data

Ontonagon County, At a glance

Ontonagon County at a glance

Predicted: EPA radon zone

EPA Zone 3: lower predicted potential

is EPA's lowest class, and its forecast for Ontonagon County as a whole is an average indoor of less than 2 pCi/L (less than 75 Bq/m³). A low zone clears no address in it: homes above EPA's turn up in all three zones.

USGS geologic potential: Low across 63% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Ontonagon County, 2008 to 2017, laboratory
Under 2 pCi/L: 73%2 to 4 pCi/L: 15%4 pCi/L and above: 12%

Of 123 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Ontonagon County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L9073.2%
2 to 4 pCi/L1915.4%
4 pCi/L and above1411.4%
What these figures count

These are the 123 tests reported to CDC for Ontonagon 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

Ontonagon County, Compared

Ontonagon County radon figures, compared

Calculated by Radon411

Ontonagon County reports fewer high tests than Michigan overall. 11.4% of its 123 tests over the 2008 to 2017 laboratory totals were at or above 4 pCi/L. That is 15.5 points below the 26.9% pooled from 83 Michigan counties.

Ordered from highest share down, it comes 65th of 82 Michigan counties with 30 or more tests for the same period. Nationally, every county with a figure for the same period pools to 35.7%; Ontonagon County sits 24.3 points below it.

Next door, the shares run from 10.8% in Houghton County to 36.2% in Iron County, with Houghton County below Ontonagon County. Zone 3 on EPA's map (predicted average under 2 pCi/L) and a 11.4% share point the same way here.

Half the tests came in under 1.3 pCi/L and half over it; the single highest reached 10.1 pCi/L. The rest split 73.2% under 2 pCi/L and 15.4% from 2 to 4 (Michigan: 46.4% and 26.7%).

CDC's ten-year totals for Ontonagon County went from 133 tests (2005 to 2014) to 123 (2008 to 2017), the share going from 10.5% to 11.4%.

Ontonagon County against Michigan, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Ontonagon County
Ontonagon County12311.4%1.3 pCi/LThis county
Michigan, pooled83 counties, pooled114,40726.9%Not pooled+15.5 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+24.3 points
Lenawee Countyhighest in the state1,90756.7%4.6 pCi/L+45.3 points
Muskegon Countylowest in the state6293.2%1.2 pCi/L−8.2 points
Iron County, MIborders it26536.2%2.6 pCi/L+24.8 points
Gogebic County, MIborders it17112.9%1.2 pCi/L+1.5 points
Houghton County, MIborders it1,09310.8%1.1 pCi/L−0.6 points
Where Ontonagon County's reported results fell, 2008 to 2017, laboratory, beside Michigan and the United States
ResultOntonagon County testsOntonagon County shareMichigan shareU.S. shareAgainst Michigan
Under 2 pCi/L9073.2%46.4%39.6%+26.8 points
2 to 4 pCi/L1915.4%26.7%24.7%−11.3 points
4 pCi/L and above1411.4%26.9%35.7%−15.5 points
Ontonagon 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
Roscommon County60 of 8216612.7%1.0 pCi/L
Antrim County61 of 8234312.0%1.5 pCi/L
Menominee County62 of 8212011.7%1.2 pCi/L
Chippewa County63 of 8231911.6%0.9 pCi/L
Grand Traverse County64 of 821,61411.5%1.4 pCi/L
Ontonagon County65 of 8212311.4%1.3 pCi/L
Baraga County66 of 8216311.0%1.1 pCi/L
Houghton County67 of 821,09310.8%1.1 pCi/L
Osceola County68 of 8224610.6%1.7 pCi/L
Charlevoix County69 of 825029.8%1.4 pCi/L
Wexford County70 of 826219.7%1.5 pCi/L
Ontonagon County ten-year laboratory totals, against Michigan's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestMichigan, pooledChange from the row before
2008 to 201712311.4%1.3 pCi/L10.1 pCi/L26.9%+1.1 points
2007 to 201611710.3%1.1 pCi/L10.1 pCi/L26.8%Level
2006 to 201511710.3%1.1 pCi/L10.1 pCi/L26.8%−0.2 points
2005 to 201413310.5%0.9 pCi/L13.4 pCi/L26.2%First on file

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

Ontonagon County, State data

Michigan's own radon test data

Measured

What Michigan's own agencies publish about radon tests in Ontonagon 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 Ontonagon County

Michigan EGLE publishes its figures by ZIP code, not by county. These are the 9 ZIP codes that lie wholly or partly in Ontonagon County, each with the state's own figures for it. Period: About 10 years to 2026-05-15.

ZIP codes in Ontonagon County
ZIP codeWhat the state reports
499102 tests, figures not shown
499123 tests, figures not shown
499252 tests, figures not shown
499473 tests, figures not shown
499483 tests, figures not shown
499534% greater than 4 pCi/L, median 1.1 pCi/L, 56 tests
499601 tests, figures not shown
4996517% greater than 4 pCi/L, median 0.9 pCi/L, 6 tests
499670% greater than 4 pCi/L, median 0.0 pCi/L, 5 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.

Ontonagon County, Geology

The ground under Ontonagon County

Predicted

USGS's geologic map splits Ontonagon County: 63.1% of its land is low radon potential and 36.9% moderate. The map puts 63.1% of Ontonagon County in the area it calls Glacial Lakes and 36.9% in Marquette Highland/Keweenaw Peninsula/Gogebic Range. USGS gives the first a radon index of 7, in the low band (5 to 8), and the second 11, in the moderate band (9 to 11).

USGS's geologic areas under Ontonagon County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Glacial LakesSilt and clay glacial lake deposits.Low763.1%
Marquette Highland/Keweenaw Peninsula/Gogebic RangeGranite, iron formtion, sandstone, conglomerate, metamorphic rocks, and glacial drift.Moderate1136.9%

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

Ontonagon County beside the ground around it

Across Michigan 9.6% of the land is rated high; none of Ontonagon County's is. Every one of the 3 counties that border it has more moderate-potential ground, Iron County the most at 100%.

Share of land by USGS radon potential: Ontonagon County, the 3 counties bordering it and Michigan
AreaEPA zoneLow potentialModerate potentialHigh potential
Ontonagon CountyZone 363.1%36.9%None
Gogebic CountyZone 216.3%83.7%None
Houghton CountyZone 216.2%81.1%None
Iron CountyZone 2None100%None
Michigan83 counties, pooled by land areaVaries45.0%44.3%9.6%

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

Local help

Ontonagon County, Local resources

Radon testing and mitigation in Ontonagon County

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

Ontonagon County, Questions

Questions about radon in Ontonagon County

Are radon levels high in Ontonagon County?

Over the 2008 to 2017 laboratory totals, 11.4% of the radon tests reported to CDC for Ontonagon County, Michigan were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.3 pCi/L. Of 82 Michigan counties with 30 or more tests for the same period, 64 reported a higher share; pooled, the state comes to 26.9%.

Which counties border Ontonagon County?

Ontonagon County borders 3 counties: Gogebic County, Houghton County and Iron County.

Products

Ontonagon County, Products

Testing a home in Ontonagon County

In Ontonagon County, 11.4% of 123 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 26.9% pooled across Michigan. Zone 3 is the lowest label, yet homes at or above 4 pCi/L occur in every zone: a short-term kit (2 to 90 days) is the quick first check in Ontonagon County.

Test kits and monitors3

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Best radon monitors for Ontonagon County homes, compared

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Ontonagon County, Bordering counties

Counties bordering Ontonagon County

Calculated by Radon411

Ontonagon County, Cities and towns

Cities and towns in Ontonagon County

Ontonagon County's population has barely moved since 2020: 5,823 residents on July 1, 2025 against 5,799 then, by the Census Bureau's estimates. Spread over its land, that is 4.4 people to the square mile. Ontonagon, its one incorporated place, has 1,264 residents, 21.7% of the total. Testing is reported here more often than across the state: CDC's 123 reported tests for 2008 to 2017 come to 21.1 for every 1,000 residents (2025 estimate), against 11.3 for Michigan.

Ontonagon is the one incorporated place here; CDC publishes no figure by town, so it reads Ontonagon County's.

Ontonagon, Ontonagon County: residents on July 1, 2025
PlaceResidentsSince 2020Share of residents
Ontonagon1,264+0.3%21.7%

One incorporated place, 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).

Ontonagon County, Homes

Homes in Ontonagon County

Ontonagon County is a place of houses on their own lots: 90% of its 5,256 homes are detached single-family houses, against 72% across Michigan. The homes are older than Michigan's as a whole: half were built before 1962 (1972 for Michigan), and 48% date from before 1960. Owners live in 87% of the occupied homes (Michigan: 73%), so for most households a test and a fix are their own to order.

Homes in Ontonagon County, Michigan, 2019 to 2023
HomesOntonagon CountyMichigan
Housing units5,2564,599,683
Detached houses90%72%
In buildings of 5 or more2%13%
Mobile homes5%5%
Built before 196048%36%
Built since 20009%15%
Middle year built19621972
Owner-occupied87%73%

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