Iowa Radon Data • Updated November 2026
Iowa Radon Levels by County: All 99 Counties Ranked.
Average radon test results for every Iowa county, from Sioux County at 13.6 pCi/L to Decatur County at 3.2 pCi/L, with central Iowa highlighted. Here's what the numbers mean, and what they can't tell you about your own home.
Test Your Home's Radon LevelIowa Average
8.5 pCi/L
U.S. Average
1.3 pCi/L
Counties at or above 4.0
94 of 99
Highest: Sioux
13.6 pCi/L
Polk County
7.3 pCi/L
County figures: CDC National Environmental Public Health Tracking Network, mean pre-mitigation radon level by county, tests reported 2008–2017. Iowa and U.S. averages: Iowa HHS Radon Home Buyers and Sellers Fact Sheet. EPA action level: 4.0 pCi/L.
Every Iowa County, Ranked
The table lists all 99 Iowa counties by their mean pre-mitigation radon level, the average of tests reported to the CDC Tracking Network before any mitigation system was installed, over the ten years from 2008 through 2017.
The teal bar shows each county relative to the highest county. The gold marker is the EPA action level of 4.0 pCi/L. Only five counties fall below it, and even those sit within a fraction of a picocurie of the line.
Central Iowa counties are highlighted. Polk County, with more reported tests than any other county in the state, averages 7.3 pCi/L.
Why do these numbers run high? Iowa's glacial soils are the reason. Read why Iowa has the highest radon in the country →
| # | County | Mean pCi/L | EPA 4.0 |
|---|---|---|---|
| 1 | Sioux | 13.6 | Above |
| 2 | Adair | 13.3 | Above |
| 3 | Audubon | 12.1 | Above |
| 4 | Clay | 12 | Above |
| 5 | Jasper Central Iowa | 11.8 | Above |
| 6 | Guthrie Central Iowa | 11.2 | Above |
| 7 | Marshall Central Iowa | 11.2 | Above |
| 8 | O'Brien | 11 | Above |
| 9 | Shelby | 11 | Above |
| 10 | Tama | 10.7 | Above |
| 11 | Cass | 10.6 | Above |
| 12 | Cherokee | 10.6 | Above |
| 13 | Plymouth | 10.4 | Above |
| 14 | Carroll | 10.3 | Above |
| 15 | Montgomery | 10.2 | Above |
| 16 | Lyon | 10 | Above |
| 17 | Pocahontas | 9.9 | Above |
| 18 | Sac | 9.9 | Above |
| 19 | Dickinson | 9.7 | Above |
| 20 | Fremont | 9.7 | Above |
| 21 | Greene | 9.7 | Above |
| 22 | Poweshiek | 9.7 | Above |
| 23 | Allamakee | 9.6 | Above |
| 24 | Buena Vista | 9.6 | Above |
| 25 | Crawford | 9.6 | Above |
| 26 | Ida | 9.5 | Above |
| 27 | Grundy | 9.4 | Above |
| 28 | Osceola | 9.4 | Above |
| 29 | Page | 9.4 | Above |
| 30 | Adams | 9.2 | Above |
| 31 | Monona | 9.2 | Above |
| 32 | Madison Central Iowa | 9.1 | Above |
| 33 | Winneshiek | 9.1 | Above |
| 34 | Winnebago | 9 | Above |
| 35 | Hancock | 8.9 | Above |
| 36 | Clayton | 8.8 | Above |
| 37 | Emmet | 8.8 | Above |
| 38 | Warren Central Iowa | 8.8 | Above |
| 39 | Wright | 8.8 | Above |
| 40 | Howard | 8.7 | Above |
| 41 | Mitchell | 8.7 | Above |
| 42 | Benton | 8.6 | Above |
| 43 | Humboldt | 8.6 | Above |
| 44 | Calhoun | 8.5 | Above |
| 45 | Franklin | 8.5 | Above |
| 46 | Marion Central Iowa | 8.5 | Above |
| 47 | Union | 8.4 | Above |
| 48 | Mills | 8.3 | Above |
| 49 | Harrison | 8.1 | Above |
| 50 | Webster | 8.1 | Above |
| 51 | Kossuth | 8 | Above |
| 52 | Worth | 8 | Above |
| 53 | Palo Alto | 7.9 | Above |
| 54 | Woodbury | 7.9 | Above |
| 55 | Fayette | 7.8 | Above |
| 56 | Hamilton | 7.8 | Above |
| 57 | Jones | 7.8 | Above |
| 58 | Boone Central Iowa | 7.7 | Above |
| 59 | Taylor | 7.7 | Above |
| 60 | Hardin | 7.5 | Above |
| 61 | Iowa | 7.4 | Above |
| 62 | Chickasaw | 7.3 | Above |
| 63 | Polk Central Iowa | 7.3 | Above |
| 64 | Buchanan | 7.2 | Above |
| 65 | Des Moines | 7.2 | Above |
| 66 | Keokuk | 7.2 | Above |
| 67 | Floyd | 7.1 | Above |
| 68 | Cedar | 7 | Above |
| 69 | Mahaska | 7 | Above |
| 70 | Butler | 6.9 | Above |
| 71 | Washington | 6.9 | Above |
| 72 | Bremer | 6.7 | Above |
| 73 | Cerro Gordo | 6.7 | Above |
| 74 | Dallas Central Iowa | 6.7 | Above |
| 75 | Jackson | 6.6 | Above |
| 76 | Henry | 6.5 | Above |
| 77 | Story Central Iowa | 6.5 | Above |
| 78 | Louisa | 6.4 | Above |
| 79 | Pottawattamie | 6.4 | Above |
| 80 | Lucas | 6.3 | Above |
| 81 | Clinton | 6 | Above |
| 82 | Delaware | 5.6 | Above |
| 83 | Dubuque | 5.6 | Above |
| 84 | Black Hawk | 5.5 | Above |
| 85 | Davis | 5.3 | Above |
| 86 | Lee | 5.3 | Above |
| 87 | Muscatine | 5 | Above |
| 88 | Scott | 4.9 | Above |
| 89 | Clarke | 4.8 | Above |
| 90 | Linn | 4.8 | Above |
| 91 | Johnson | 4.7 | Above |
| 92 | Appanoose | 4.4 | Above |
| 93 | Wayne | 4.1 | Above |
| 94 | Jefferson | 4 | Above |
| 95 | Wapello | 3.9 | Below |
| 96 | Ringgold | 3.8 | Below |
| 97 | Monroe | 3.7 | Below |
| 98 | Van Buren | 3.7 | Below |
| 99 | Decatur | 3.2 | Below |
Central Iowa Counties
The Des Moines metro and the counties around it span a wide range. Jasper, Guthrie, and Marshall counties rank in the top ten statewide at over 11 pCi/L. Polk, Dallas, and Story counties sit closer to the middle of the pack, between 6.5 and 7.3 pCi/L.
Every one of these counties averages above the EPA action level. If you live in Ankeny, West Des Moines, Waukee, or Norwalk, the county you're in tells you the odds are not in your favor. A test tells you the answer.
If your home tests high, radon mitigation in Des Moines and the surrounding counties is a one-day install that brings levels down permanently.
Mean Radon Level, 2008–2017
- Jasper County #5 of 9911.8 pCi/L
- Guthrie County #6 of 9911.2 pCi/L
- Marshall County #7 of 9911.2 pCi/L
- Madison County #32 of 999.1 pCi/L
- Warren County #38 of 998.8 pCi/L
- Marion County #46 of 998.5 pCi/L
- Boone County #58 of 997.7 pCi/L
- Polk County #63 of 997.3 pCi/L
- Dallas County #74 of 996.7 pCi/L
- Story County #77 of 996.5 pCi/L
What a County Average Does, and Doesn't, Tell You
A county mean is a useful picture of regional risk. It is not a prediction for any one house. Iowa HHS is direct about this: radon levels "can vary considerably from house to house, even on the same street and neighborhood," and "a high and low level of radon can be found in homes directly next to each other."
The reasons are local. How a home was built, whether it has a basement or a crawl space, how the foundation has settled, where the sump pit sits, and how the house breathes in winter all change how much soil gas gets pulled inside. Two identical floor plans on the same block can test very differently.
That is why the EPA, Iowa HHS, the American Lung Association, and the Surgeon General all recommend testing every home, in every zone, regardless of the county number. A certified 48- to 72-hour test is the only measurement that applies to your address.
Three things the table can tell you
- OddsA county averaging 9 pCi/L has a larger share of elevated homes than one averaging 5. Your odds are worse, not your result.
- ScaleWhere averages run into double digits, elevated homes are often very elevated. Sioux, Adair, and Jasper counties are examples.
- FloorThe lowest county in Iowa still averages 3.2 pCi/L, more than double the U.S. average. There is no low-radon county in Iowa.
Why Zip-Code Radon Maps Mislead
Finer-grained data looks more precise. It isn't precise about your home.
The data exists.
Iowa HHS publishes aggregate radon test data by county and by ZIP code, drawn from tests in private homes and real estate transactions that met the criteria for a valid test. It's a legitimate public resource.
A ZIP is still an average.
A ZIP code covers thousands of homes on different soils, foundations, and construction eras. Its average carries the same house-to-house variation Iowa HHS warns about, just over a smaller map. Fewer tests per ZIP also make the number noisier, not sharper.
Nobody can predict your house.
No map, model, or neighbor's result substitutes for a test in your home. Be cautious of any claim that a specific street or property is "safe" or "high" without a measurement taken there.
Iowa Radon Levels — Common Questions
What is the average radon level in Iowa?
The Iowa Department of Health and Human Services puts the average indoor radon level in Iowa at 8.5 pCi/L, compared with 1.3 pCi/L for the United States as a whole. The EPA recommends fixing a home at 4.0 pCi/L or higher, so the typical Iowa home is more than double the action level.
What is the average radon level in Polk County?
Tests reported to the CDC Tracking Network from 2008 through 2017 give Polk County a mean pre-mitigation radon level of 7.3 pCi/L. That is below the Iowa statewide figure but still well above the EPA action level of 4.0 pCi/L. Polk County has more reported tests than any other Iowa county, so its average rests on a large sample.
Which Iowa county has the highest radon?
Among all 99 counties, Sioux County in northwest Iowa shows the highest mean at 13.6 pCi/L in the 2008–2017 CDC data, followed closely by Adair County at 13.3 pCi/L. Decatur County in south-central Iowa is lowest at 3.2 pCi/L. Even the lowest county average is close to the EPA action level.
Can I look up radon levels by zip code in Iowa?
Iowa HHS publishes aggregate test data by county and by ZIP code. Those files are useful for seeing regional patterns, but a ZIP-code average is still not a measurement of your house. Iowa HHS notes that a high and a low reading can be found in homes directly next to each other. The only way to know your own level is a test in your own home.
My county average is below 4.0. Do I still need to test?
Yes. Every Iowa county is in EPA Zone 1, the highest-risk classification, and Iowa HHS estimates that as many as 5 in 7 Iowa homes have elevated radon. A county average below 4.0 pCi/L means many homes in that county still test above it. Averages describe a county, not a house.
Sources
- CDC National Environmental Public Health Tracking Network — Mean pre-mitigation radon level (pCi/L) by county, Iowa, tests reported 2008–2017. All county figures on this page.
- Iowa Radon Home Buyers and Sellers Fact Sheet — Iowa HHS. Statewide average of 8.5 pCi/L, U.S. average of 1.3 pCi/L, Zone 1 designation, house-to-house variation, and the 5-in-7 estimate.
- Iowa HHS Radon Program — County and ZIP-code aggregate data files, credentialed specialist lists, and the Iowa Radon Hotline (1-800-383-5992).
The county average is the odds. The test is the answer.
A certified 48- to 72-hour test tells you exactly what your family is breathing, with results the same day we pick up the monitor.