Long-term kit
RL416 long-term radon test kit, lab fee included
- Lab fee included
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Marshall County, Iowa
EPA puts Marshall County in Zone 1, its highest radon zone, and high results are common there: 70.2% of the 570 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
Share at 4+ pCi/L
70.2%
11.7 pts above IA
- Marshall
- 70.2%
- Iowa
- 58.5%
570 tests, 2008 to 2017
Median result
8.2pCi/L
Action level reached
- Marshall
- 8.2 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
570
41st of 99 by tests
- Marshall
- 570
- Polk
- 10,945
Reported to CDC before any fix, 2008 to 2017
EPA radon zone
Zone 1
Highest potential
- Zone 1
- 2
- 3
1 highest, 3 lowest
EPA predicts over 4 pCi/L indoors
Rank in Iowa
29 of 99
Middle half
- Marshall
- 70.2%
- Sioux
- 84.2%
By share, of 99 with 30+ tests
Read a result for Marshall County
Starts at Marshall County's median, 8.2 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 8.2 pCi/L
At or above 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Marshall County's median reported result, 2008 to 2017.
The data
Marshall County, At a glance
Marshall County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Marshall County in
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 Marshall County, 2008 to 2017, laboratory
Under 2 pCi/L: 15%2 to 4 pCi/L: 15%4 pCi/L and above: 70%
Of 570 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 87 | 15.3% |
| 2 to 4 pCi/L | 83 | 14.6% |
| 4 pCi/L and above | 400 | 70.2% |
What these figures count
These are the 570 tests reported to CDC for Marshall 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).
Marshall County, Compared
Marshall County radon figures, compared
Calculated by Radon411More than half: 70.2% of the 570 radon tests reported to CDC for Marshall County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 29th of 99 Iowa counties with 30 or more tests for the same period. That is 11.7 points above the 58.5% pooled from 99 Iowa counties.
The median result, 8.2 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 100.8 pCi/L. The rest split 15.3% under 2 pCi/L and 14.6% from 2 to 4 (Iowa: 21.8% and 19.7%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 70.2% share point the same way here.
2 of its 6 bordering counties with figures ran higher, led by Jasper County at 73.3%; Story County reported 59.9%. Statewide for the same period, Sioux County reported the highest share (84.2%) and Decatur County the lowest (25.9%).
CDC's ten-year totals for Marshall County went from 434 tests (2005 to 2014) to 570 (2008 to 2017), the share going from 73.3% to 70.2%.
Nationally, every county with a figure for the same period pools to 35.7%; Marshall County sits 34.5 points above it. CDC also counts 81 tests taken after mitigation in Marshall County for the same period: tests in homes where a fix was already in.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Marshall County, Geology
The ground under Marshall County
PredictedUSGS's geologic map puts all of Marshall County's mapped land in one class: high radon potential. 99.2% of it lies in the area the map calls Loess-Covered Drift Plains, to which USGS gives a radon index of 13, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Loess-Covered Drift Plains | Pre-Illinoian and Illinoian glacial deposits, and loess. | High | 13 | 99.2% |
| Des Moines Lobe | Calcareous loamy till derived from shale, limestone, dolomite, sandstone. | High | 12 | 0.8% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Marshall County beside the ground around it
On high-potential ground Marshall County is close to Iowa as a whole: 100% of its land against 98.8%. Of the 6 counties that border it, none has as large a share of high-potential ground; Hardin County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Marshall County, Local resources
Radon testing and mitigation in Marshall County
Listed radon businesses with an address in Marshall County:
- Iowa HHS Radon ProgramIowa HHS Radon Program, run by Iowa Department of Health and Human Services, licenses or certifies radon professionals, offers free or discounted test kits and states the rule for disclosing radon when a home is sold, and answers questions about testing and mitigation in Iowa.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
You can reach the Hotline by calling 1-800-383-5992 to order low-cost radon test kits and find answers to your radon questions.
- Compare kits
- Professionals in Iowa185 professionals are listed in Iowa.
Listed radon professionals by town: Marshalltown, Liscomb
What Iowa's program says
- Phone
- (515) 281-4928
- Licensing of radon professionals
Iowa’s radon program approves applications for persons who wish to become certified to perform radon testing or credentialed to perform mitigation and laboratories that provide radon testing devices and analytical services.
- Disclosure when a home is sold or rented
However, per Iowa Code chapters 543B.9 and 543B.18 and Iowa Administrative Code 193E Chapter 14 administered by the Iowa Real Estate Commission, a seller must disclose any known tests for the presence of radon and if yes, provide the date of last report and the result(s).
What it means
Marshall County, Questions
Questions about radon in Marshall County
Are radon levels high in Marshall County?
Over the 2008 to 2017 laboratory totals, 70.2% of the radon tests reported to CDC for Marshall County, Iowa were at or above 4 pCi/L, and the median reported pre-mitigation result was 8.2 pCi/L. Of 99 Iowa counties with 30 or more tests for the same period, 28 reported a higher share; pooled, the state comes to 58.5%.
Which counties border Marshall County?
Marshall County borders 6 counties: Jasper County, Story County, Tama County, Hardin County, Grundy County and Poweshiek County.
Products
Marshall County, Products
Testing a home in Marshall County
In Marshall County, 70.2% of 570 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 58.5% pooled across Iowa. In Zone 1 the year-round level in Marshall 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 monitorMonitorSafetySiren
Pro4 plug-in radon detector with a display and alarm
- C-NRPP 2024/25: Not included
- Plug-in
- Alarm
- Screen
First reading: Within 48 hours
Short-term kit
Radon Short Term Test Kit short-term charcoal radon test kit, lab fee included
- Lab fee included
Method: Charcoal
In home: 2 to 7 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Marshall County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Marshall County
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Marshall County, Bordering counties
Counties bordering Marshall County
Calculated by Radon411- Radon levels in Jasper CountyEPA zone 1
73.3%at or above 4 pCi/L
Median 8.2 pCi/L · 746 tests · 3.1 points above Marshall County
- Radon levels in Poweshiek CountyEPA zone 1
70.6%at or above 4 pCi/L
Median 7.2 pCi/L · 419 tests · 0.4 points above Marshall County
- Radon levels in Tama CountyEPA zone 1
67.9%at or above 4 pCi/L
Median 7.0 pCi/L · 333 tests · 2.3 points below Marshall County
- Radon levels in Grundy CountyEPA zone 1
66.9%at or above 4 pCi/L
Median 6.9 pCi/L · 501 tests · 3.3 points below Marshall County
- Radon levels in Hardin CountyEPA zone 1
62.8%at or above 4 pCi/L
Median 5.6 pCi/L · 349 tests · 7.4 points below Marshall County
- Radon levels in Story CountyEPA zone 1
59.9%at or above 4 pCi/L
Median 5.0 pCi/L · 2,568 tests · 10.3 points below Marshall County
Marshall County, Cities and towns
Cities and towns in Marshall County
About 39,890 people live in Marshall County by the Census Bureau's estimate for July 1, 2025, 210 fewer than in 2020 (−0.5%). That works out to 70 people per square mile of land. Marshalltown alone is home to 27,536 of them, 69.0% of the total. Reported testing is thin here: 570 tests over 2008 to 2017, or 14.3 for every 1,000 residents (2025 estimate), where Iowa as a whole comes to 29.4.
From Marshalltown to St. Anthony, CDC publishes no figure by town: each reads Marshall County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Marshalltown | 27,536 | −0.2% | 69.0% |
| State Center | 1,389 | −0.6% | 3.5% |
| Le Grandextends beyond Marshall County | 883 | −1.9% | Counted whole |
| Melbourne | 760 | −3.6% | 1.9% |
| Gilman | 527 | −3.1% | 1.3% |
| Albion | 438 | −3.1% | 1.1% |
| Liscomb | 288 | −0.3% | 0.7% |
| Rhodes | 265 | −1.1% | 0.7% |
| Laurel | 211 | −0.9% | 0.5% |
| Haverhill | 162 | −2.4% | 0.4% |
| Clemons | 132 | −4.3% | 0.3% |
| Ferguson | 97 | −1.0% | 0.2% |
- St. Anthony
13 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 Marshall County is counted whole, so it has no share.
Marshall County, Homes
Homes in Marshall County
Marshall County is a place of houses on their own lots: 78% of its 16,860 homes are detached single-family houses, against 72% across Iowa. The homes are older than Iowa's as a whole: half were built before 1958 (1971 for Iowa), and 53% date from before 1960. 73% of occupied homes are lived in by their owner (Iowa: 72%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Marshall County | Iowa |
|---|---|---|
| Housing units | 16,860 | 1,427,175 |
| Detached houses | 78% | 72% |
| In buildings of 5 or more | 10% | 14% |
| Mobile homes | 3% | 3% |
| Built before 1960 | 53% | 39% |
| Built since 2000 | 10% | 21% |
| Middle year built | 1958 | 1971 |
| Owner-occupied | 73% | 72% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.