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Radon Levels in Lyon County, Iowa

EPA puts Lyon County in Zone 1, its highest radon zone, and high results are common there: 77.6% of the 237 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

    77.6%

    19.1 pts above IA

    Lyon
    77.6%
    Iowa
    58.5%

    237 tests, 2008 to 2017

  • Median result

    8.3pCi/L

    Action level reached

    Lyon
    8.3 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    237

    77th of 99 by tests

    Lyon
    237
    Polk
    10,945

    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 Iowa

    7 of 99

    Top quarter

    Lyon
    77.6%
    Sioux
    84.2%

    By share, of 99 with 30+ tests

Read a result for Lyon County

Starts at Lyon County's median, 8.3 pCi/L

8.3pCi/L

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

EPA’s reading of 8.3 pCi/L

At or above 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 at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Lyon County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Lyon County, At a glance

Lyon County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Lyon 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 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

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

Reported results by concentration band, Lyon County, 2008 to 2017, laboratory
Under 2 pCi/L: 6%2 to 4 pCi/L: 16%4 pCi/L and above: 78%

Of 237 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Lyon County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L145.9%
2 to 4 pCi/L3916.5%
4 pCi/L and above18477.6%
What these figures count

These are the 237 tests reported to CDC for Lyon 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

Lyon County, Compared

Lyon County radon figures, compared

Calculated by Radon411

More than half: 77.6% of the 237 radon tests reported to CDC for Lyon County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 7th of 99 Iowa counties with 30 or more tests for the same period. That is 19.1 points above the 58.5% pooled from 99 Iowa counties.

The median result, 8.3 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 39.4 pCi/L. The rest split 5.9% under 2 pCi/L and 16.5% from 2 to 4 (Iowa: 21.8% and 19.7%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 77.6% share point the same way here.

3 of its 7 bordering counties with figures ran higher, led by Sioux County at 84.2%; Lincoln County, SD reported 56.5%. 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 Lyon County went from 176 tests (2005 to 2014) to 237 (2008 to 2017), the share going from 75.6% to 77.6%.

Nationally, every county with a figure for the same period pools to 35.7%; Lyon County sits 41.9 points above it. CDC also counts 6 tests taken after mitigation in Lyon County for the same period: tests in homes where a fix was already in.

Lyon County against Iowa, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Lyon County
Lyon County23777.6%8.3 pCi/LThis county
Iowa, pooled99 counties, pooled95,24558.5%Not pooled−19.1 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−41.9 points
Plymouth Countyhighest in the state1,40582.3%8.6 pCi/L+4.7 points
Decatur Countylowest in the state8525.9%2.5 pCi/L−51.7 points
Sioux County, IAborders it1,98284.2%10.7 pCi/L+6.6 points
Rock County, MNborders it21083.8%7.7 pCi/L+6.2 points
O'Brien County, IAborders it65281.7%8.9 pCi/L+4.1 points
Nobles County, MNborders it26770.4%7.0 pCi/L−7.2 points
Osceola County, IAborders it12267.2%6.8 pCi/L−10.4 points
Minnehaha County, SDborders it1,92058.5%4.8 pCi/L−19.1 points
Lincoln County, SDborders it79556.5%4.7 pCi/L−21.1 points
Where Lyon County's reported results fell, 2008 to 2017, laboratory, beside Iowa and the United States
ResultLyon County testsLyon County shareIowa shareU.S. shareAgainst Iowa
Under 2 pCi/L145.9%21.8%39.6%−15.9 points
2 to 4 pCi/L3916.5%19.7%24.7%−3.2 points
4 pCi/L and above18477.6%58.5%35.7%+19.1 points
Lyon County ranked among the 99 Iowa counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Plymouth County2 of 991,40582.3%8.6 pCi/L
O'Brien County3 of 9965281.7%8.9 pCi/L
Clay County4 of 9974479.4%9.6 pCi/L
Shelby County5 of 9985778.4%9.0 pCi/L
Audubon County6 of 9918978.3%9.5 pCi/L
Lyon County7 of 9923777.6%8.3 pCi/L
Carroll County8 of 9959477.6%7.8 pCi/L
Cass County9 of 9932777.4%8.1 pCi/L
Sac County10 of 9949176.6%7.0 pCi/L
Crawford County11 of 9937374.8%7.0 pCi/L
Monona County12 of 9960374.6%7.0 pCi/L
Lyon County ten-year laboratory totals, against Iowa's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIowa, pooledChange from the row before
2008 to 201723777.6%8.3 pCi/L39.4 pCi/L58.5%+3.0 points
2007 to 201620574.6%7.4 pCi/L31.9 pCi/L58.6%+0.9 points
2006 to 201519873.7%7.3 pCi/L34.2 pCi/L59.4%−1.9 points
2005 to 201417675.6%7.5 pCi/L34.2 pCi/L59.6%First on file

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

Lyon County, Geology

The ground under Lyon County

Predicted

USGS's geologic map puts all of Lyon County's mapped land in one class: high radon potential. All 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).

USGS's geologic areas under Lyon County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Loess-Covered Drift PlainsPre-Illinoian and Illinoian glacial deposits, and loess.High1399.7%

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

Lyon County beside the ground around it

On high-potential ground Lyon County is close to Iowa as a whole: 100% of its land against 98.8%. Of the 7 counties that border it, none has as large a share of high-potential ground; Lincoln County, SD comes nearest at 100%.

Share of land by USGS radon potential: Lyon County, the 7 counties bordering it and Iowa
AreaEPA zoneLow potentialModerate potentialHigh potential
Lyon CountyZone 1NoneNone100%
Sioux CountyZone 1NoneNone100%
Rock County, MNZone 1NoneNone100%
Lincoln County, SDZone 1NoneNone100%
Osceola CountyZone 1NoneNone100%
Nobles County, MNZone 1NoneNone100%
O'Brien CountyZone 1NoneNone100%
Minnehaha County, SDZone 1NoneNone99.9%
Iowa99 counties, pooled by land areaVariesNone1.2%98.8%

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

Local help

Lyon County, Local resources

Radon testing and mitigation in Lyon County

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

Lyon County, Questions

Questions about radon in Lyon County

Are radon levels high in Lyon County?

Over the 2008 to 2017 laboratory totals, 77.6% of the radon tests reported to CDC for Lyon County, Iowa were at or above 4 pCi/L, and the median reported pre-mitigation result was 8.3 pCi/L. Of 99 Iowa counties with 30 or more tests for the same period, 6 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Lyon County?

Lyon County borders 7 counties: Sioux County, IA, Rock County, MN, Lincoln County, SD, Osceola County, IA, Nobles County, MN, O'Brien County, IA and Minnehaha County, SD.

Products

Lyon County, Products

Testing a home in Lyon County

In Lyon County, 77.6% of 237 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 Lyon 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

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

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Lyon County, Bordering counties

Counties bordering Lyon County

Calculated by Radon411

Lyon County, Cities and towns

Cities and towns in Lyon County

The Census Bureau estimates 12,354 residents in Lyon County for July 1, 2025, 430 more than in 2020 (+3.6%). That works out to 21 people per square mile of land. Its largest town, Rock Rapids, has 2,733 residents, 22.1% of the total. Together its 8 incorporated places hold 59.5% of those residents; the other 40.5% live outside any of them. Reported testing is thin here: 237 tests over 2008 to 2017, or 19.2 for every 1,000 residents (2025 estimate), where Iowa as a whole comes to 29.4.

From Rock Rapids to Alvord, CDC publishes no figure by town: each reads Lyon County's.

The cities and towns in Lyon County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Rock Rapids2,733+4.6%22.1%
George1,093+1.2%8.8%
Inwood965+4.2%7.8%
Larchwood953+3.0%7.7%
Doon640+4.9%5.2%
Little Rock439−0.2%3.6%
Lester306+3.0%2.5%
Alvord217+3.8%1.8%

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).

Lyon County, Homes

Homes in Lyon County

Lyon County is a place of houses on their own lots: 90% of its 4,857 homes are detached single-family houses, against 72% across Iowa. Half of its homes were built before 1965, close to Iowa's 1971: 44% date from before 1960 and 17% from 2000 or later. Owners live in 83% of the occupied homes (Iowa: 72%), so for most households a test and a fix are their own to order.

Homes in Lyon County, Iowa, 2019 to 2023
HomesLyon CountyIowa
Housing units4,8571,427,175
Detached houses90%72%
In buildings of 5 or more6%14%
Mobile homes1%3%
Built before 196044%39%
Built since 200017%21%
Middle year built19651971
Owner-occupied83%72%

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