Radon in Iowa: radon map by county
EPA's Map of Radon Zones puts 99 of Iowa's 99 counties in Zone 1 (predicted average indoor radon above 4 pCi/L), 0 in Zone 2 and 0 in Zone 3. Of 68,663 building tests that radon laboratories reported for 2008 to 2017, 57.1% were at or above EPA's 4 pCi/L action level, against 36.5% nationally (number 4 of 42 states with 1,000+ tests). The highest county share is Sioux County (84.2% of 1,124 tests).
Radon by county in Iowa
| County | EPA zone | Lab tests | Median | 4+ pCi/L |
|---|---|---|---|---|
| Adair County | Zone 1 | 66 | 9.3 | 72.4% |
| Adams County | Zone 1 | 52 | 6.1 | 65.4% |
| Allamakee County | Zone 1 | 321 | 7.0 | 73.2% |
| Appanoose County | Zone 1 | 91 | 3.7 | 45.3% |
| Audubon County | Zone 1 | 132 | 9.5 | 78.3% |
| Benton County | Zone 1 | 549 | 5.6 | 62.1% |
| Black Hawk County | Zone 1 | 2,656 | 3.8 | 48.4% |
| Boone County | Zone 1 | 695 | 6.0 | 68.7% |
| Bremer County | Zone 1 | 732 | 4.3 | 53% |
| Buchanan County | Zone 1 | 393 | 4.1 | 51.2% |
| Buena Vista County | Zone 1 | 392 | 6.9 | 72.1% |
| Butler County | Zone 1 | 266 | 5.2 | 59.9% |
| Calhoun County | Zone 1 | 303 | 6.1 | 69.8% |
| Carroll County | Zone 1 | 399 | 7.8 | 77.6% |
| Cass County | Zone 1 | 218 | 8.1 | 77.4% |
| Cedar County | Zone 1 | 616 | 5.0 | 60.4% |
| Cerro Gordo County | Zone 1 | 1,046 | 4.8 | 59% |
| Cherokee County | Zone 1 | 428 | 7.6 | 74.5% |
| Chickasaw County | Zone 1 | 322 | 4.9 | 59% |
| Clarke County | Zone 1 | 95 | 3.5 | 45.8% |
| Clay County | Zone 1 | 464 | 9.6 | 79.4% |
| Clayton County | Zone 1 | 212 | 5.8 | 62.6% |
| Clinton County | Zone 1 | 1,107 | 4.3 | 52.7% |
| Crawford County | Zone 1 | 223 | 7.0 | 74.8% |
| Dallas County | Zone 1 | 1,685 | 4.9 | 58.5% |
| Davis County | Zone 1 | 59 | 3.1 | 42.4% |
| Decatur County | Zone 1 | 61 | 2.5 | 25.9% |
| Delaware County | Zone 1 | 370 | 4.0 | 50% |
| Des Moines County | Zone 1 | 335 | 4.2 | 51.1% |
| Dickinson County | Zone 1 | 516 | 7.0 | 70.3% |
| Dubuque County | Zone 1 | 3,421 | 3.6 | 46.8% |
| Emmet County | Zone 1 | 246 | 6.3 | 71% |
| Fayette County | Zone 1 | 474 | 5.6 | 62.7% |
| Floyd County | Zone 1 | 410 | 5.1 | 59.5% |
| Franklin County | Zone 1 | 219 | 6.2 | 73.5% |
| Fremont County | Zone 1 | 122 | 7.2 | 69.8% |
| Greene County | Zone 1 | 111 | 6.2 | 71.3% |
| Grundy County | Zone 1 | 359 | 6.9 | 66.9% |
| Guthrie County | Zone 1 | 163 | 6.9 | 70.8% |
| Hamilton County | Zone 1 | 186 | 5.5 | 64.3% |
| Hancock County | Zone 1 | 367 | 5.5 | 64.5% |
| Hardin County | Zone 1 | 275 | 5.6 | 62.8% |
| Harrison County | Zone 1 | 216 | 6.2 | 69.8% |
| Henry County | Zone 1 | 120 | 3.4 | 46.4% |
| Howard County | Zone 1 | 238 | 5.9 | 61.3% |
| Humboldt County | Zone 1 | 242 | 7.0 | 70.1% |
| Ida County | Zone 1 | 234 | 7.4 | 71.7% |
| Iowa County | Zone 1 | 421 | 5.1 | 59.2% |
| Jackson County | Zone 1 | 792 | 4.1 | 52.7% |
| Jasper County | Zone 1 | 531 | 8.2 | 73.3% |
| Jefferson County | Zone 1 | 497 | 2.6 | 33.5% |
| Johnson County | Zone 1 | 6,142 | 3.2 | 41.6% |
| Jones County | Zone 1 | 459 | 5.1 | 59.3% |
| Keokuk County | Zone 1 | 156 | 5.2 | 60.3% |
| Kossuth County | Zone 1 | 262 | 5.7 | 66.1% |
| Lee County | Zone 1 | 207 | 3.2 | 43.6% |
| Linn County | Zone 1 | 7,417 | 3.0 | 39.7% |
| Louisa County | Zone 1 | 90 | 4.1 | 52.1% |
| Lucas County | Zone 1 | 65 | 3.3 | 39.3% |
| Lyon County | Zone 1 | 146 | 8.3 | 77.6% |
| Madison County | Zone 1 | 231 | 6.0 | 62.3% |
| Mahaska County | Zone 1 | 233 | 5.2 | 61.1% |
| Marion County | Zone 1 | 798 | 6.0 | 67.3% |
| Marshall County | Zone 1 | 397 | 8.2 | 70.2% |
| Mills County | Zone 1 | 327 | 6.1 | 70.1% |
| Mitchell County | Zone 1 | 274 | 6.4 | 70.7% |
| Monona County | Zone 1 | 343 | 7.0 | 74.6% |
| Monroe County | Zone 1 | 48 | 2.9 | 33.9% |
| Montgomery County | Zone 1 | 159 | 6.1 | 67.4% |
| Muscatine County | Zone 1 | 947 | 3.7 | 46.5% |
| O'Brien County | Zone 1 | 382 | 8.9 | 81.7% |
| Osceola County | Zone 1 | 85 | 6.8 | 67.2% |
| Page County | Zone 1 | 394 | 7.2 | 71.7% |
| Palo Alto County | Zone 1 | 286 | 5.9 | 70.8% |
| Plymouth County | Zone 1 | 903 | 8.6 | 82.3% |
| Pocahontas County | Zone 1 | 236 | 6.4 | 68.8% |
| Polk County | Zone 1 | 7,790 | 5.6 | 64.4% |
| Pottawattamie County | Zone 1 | 1,286 | 4.7 | 57.4% |
| Poweshiek County | Zone 1 | 312 | 7.2 | 70.6% |
| Ringgold County | Zone 1 | 67 | 2.6 | 28.7% |
| Sac County | Zone 1 | 293 | 7.0 | 76.6% |
| Scott County | Zone 1 | 3,202 | 3.3 | 44.3% |
| Shelby County | Zone 1 | 490 | 9.0 | 78.4% |
| Sioux County | Zone 1 | 1,124 | 10.7 | 84.2% |
| Story County | Zone 1 | 1,814 | 5.0 | 59.9% |
| Tama County | Zone 1 | 221 | 7.0 | 67.9% |
| Taylor County | Zone 1 | 149 | 4.6 | 60.9% |
| Union County | Zone 1 | 77 | 4.9 | 61.8% |
| Van Buren County | Zone 1 | 45 | 2.3 | 32.1% |
| Wapello County | Zone 1 | 204 | 2.7 | 35.9% |
| Warren County | Zone 1 | 1,000 | 6.3 | 66% |
| Washington County | Zone 1 | 933 | 4.6 | 54.9% |
| Wayne County | Zone 1 | 37 | 3.0 | 34.8% |
| Webster County | Zone 1 | 689 | 6.5 | 69.4% |
| Winnebago County | Zone 1 | 477 | 6.7 | 71.9% |
| Winneshiek County | Zone 1 | 579 | 6.2 | 66.4% |
| Woodbury County | Zone 1 | 2,133 | 6.1 | 69.2% |
| Worth County | Zone 1 | 118 | 6.0 | 67.5% |
| Wright County | Zone 1 | 188 | 6.2 | 66.8% |
Lab tests: buildings tested by radon laboratories, 2008 to 2017; median in pCi/L; “4+ pCi/L” is the share of tests at or above EPA's action level. n/a: no value on file (no tests, or too few to report).
What the zones mean
Zone 1 counties have a predicted average indoor radon screening level above 4 pCi/L, Zone 2 from 2 to 4 pCi/L and Zone 3 below 2 pCi/L. The prediction is from 1993 indoor measurements, geology, aerial radioactivity, soils and foundation types. EPA: “This map should not be used to determine if individual homes need to be tested.” EPA recommends fixing a home at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of exposure.
Radon in Iowa: questions
What radon zone is Iowa?
EPA's 1993 map does not give states one zone; it zones each county. In Iowa, 99 counties are Zone 1, 0 Zone 2 and 0 Zone 3. EPA says the map "should not be used to determine if individual homes need to be tested".
Which Iowa counties have the highest radon levels?
By the share of laboratory tests at or above 4 pCi/L for 2008 to 2017 (counties with 20 or more tests): Sioux County 84.2% (median 10.7 pCi/L, 1,124 tests); Plymouth County 82.3% (median 8.6 pCi/L, 903 tests); O'Brien County 81.7% (median 8.9 pCi/L, 382 tests); Clay County 79.4% (median 9.6 pCi/L, 464 tests); Shelby County 78.4% (median 9.0 pCi/L, 490 tests).
How common is high radon in Iowa?
57.1% of the 68,663 tests in the laboratory data for Iowa (2008 to 2017) were at or above 4 pCi/L; the national share was 36.5%. Buildings are tested by choice, often because of a sale or a concern, so the share describes the tests on file, not every home.
Should I test for radon in Iowa?
Yes. EPA recommends testing every home no matter where it is, fixing it at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L, because there is no known safe level of radon exposure.
States bordering Iowa
Other free hazard lookups
- Radon by county and ZIP codeEPA radon zone and the radon test results on file for any county, ZIP code or address.
- Fault lines near an addressUSGS-mapped earthquake faults within 5 miles, their age and slip rate, and the USGS seismic hazard value.
- Power lines near an addressHigh-voltage transmission lines within 1 mile from federal maps, with voltage and distance.
- Flood zone lookupThe FEMA flood zone mapped at any US address. Not an official flood zone determination.
- Superfund sites near an addressThe nearest EPA Superfund (NPL) sites and their status.
All of these, plus wetlands, FEMA hazard ratings and the federal contamination lists, are in the Environmental Records Report for any US address ($29).
Superfund sites in Iowa · Radon map of every state
Data compiled 2026-10-20. County-level screening information, not a radon measurement of any building.