Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Locations and reports
Radon Levels in Johnson County, Iowa
EPA puts Johnson County in Zone 1, its highest radon zone, and high results are common there: 41.6% of the 7,321 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
41.6%
16.9 pts below IA
- Johnson
- 41.6%
- Iowa
- 58.5%
7,321 tests, 2008 to 2017
Median result
3.2pCi/L
Below action level
- Johnson
- 3.2 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
7,321
3rd of 99 by tests
- Johnson
- 7,321
- 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
90 of 99
Lowest quarter
- Johnson
- 41.6%
- Sioux
- 84.2%
By share, of 99 with 30+ tests
Read a result for Johnson County
Starts at Johnson County's median, 3.2 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 3.2 pCi/L
Between 2 and 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is between 2 and 4 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Johnson County's median reported result, 2008 to 2017.
The data
Johnson County, At a glance
Johnson County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Johnson 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 Johnson County, 2008 to 2017, laboratory
Under 2 pCi/L: 35%2 to 4 pCi/L: 24%4 pCi/L and above: 41%
Of 7,321 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 2,531 | 34.6% |
| 2 to 4 pCi/L | 1,744 | 23.8% |
| 4 pCi/L and above | 3,046 | 41.6% |
What these figures count
These are the 7,321 tests reported to CDC for Johnson 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).
Johnson County, Compared
Johnson County radon figures, compared
Calculated by Radon411In Johnson County, about 4 in 10 reported tests over the 2008 to 2017 laboratory totals (3,046 of 7,321) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 5.9 points higher. Across 99 Iowa counties pooled together, 58.5% of tests reached that level, so Johnson County runs 16.9 points below its state.
Of 7 neighbours with a figure, 6 reported a larger share at or above 4 pCi/L and 1 a smaller one; the spread is 39.7% (Linn County) to 62.1% (Benton County). By share, Johnson County is 90th of 99 Iowa counties with 30 or more tests for the same period.
Half the tests came in under 3.2 pCi/L and half over it; the single highest reached 73.2 pCi/L. Below the action level, 2,531 tests (34.6%) came in under 2 pCi/L, against 21.8% statewide, and 1,744 tests (23.8%) fell between 2 and 4, against 19.7% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 41.6% share point the same way here. USGS geology rates 100% of the county's land high radon potential. CDC also counts 1,091 tests taken after mitigation in Johnson County for the same period: tests in homes where a fix was already in.
CDC's ten-year totals for Johnson County went from 5,415 tests (2005 to 2014) to 7,321 (2008 to 2017), the share going from 45.0% to 41.6%.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Johnson County, Geology
The ground under Johnson County
PredictedUSGS's geologic map puts all of Johnson County's mapped land in one class: high radon potential. The map puts 91.1% of Johnson County in the area it calls Loess-Covered Drift Plains and 8.9% in Iowan Surface. USGS gives the first a radon index of 13 and the second 12, both 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 | 91.1% |
| Iowan Surface | Pre-Illinoian glaical deposits and loess. | High | 12 | 8.9% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Johnson County beside the ground around it
On high-potential ground Johnson 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; Benton County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Johnson County, Local resources
Radon testing and mitigation in Johnson County
Listed radon businesses with an address in Johnson 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: Iowa City, Coralville, North Liberty, Solon, Lone Tree
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
Johnson County, Questions
Questions about radon in Johnson County
Are radon levels high in Johnson County?
Over the 2008 to 2017 laboratory totals, 41.6% of the radon tests reported to CDC for Johnson County, Iowa were at or above 4 pCi/L, and the median reported pre-mitigation result was 3.2 pCi/L. Of 99 Iowa counties with 30 or more tests for the same period, 89 reported a higher share; pooled, the state comes to 58.5%.
Which counties border Johnson County?
Johnson County borders 7 counties: Iowa County, Cedar County, Linn County, Muscatine County, Washington County, Louisa County and Benton County.
Products
Johnson County, Products
Testing a home in Johnson County
In Johnson County, 41.6% of 7,321 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 Johnson 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
MonitorAranet
Radon One battery digital radon monitor with an e-ink screen
- C-NRPP 2024/25: Not included
- Battery
- Bluetooth
- Alarm
- Screen, app
Method: Ion chamber
First reading: Within 10 minutes
Short-term kitKidde
442020 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 3 days
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Johnson County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Johnson County
Explore
Johnson County, Bordering counties
Counties bordering Johnson County
Calculated by Radon411- Radon levels in Benton CountyEPA zone 1
62.1%at or above 4 pCi/L
Median 5.6 pCi/L · 696 tests · 20.5 points above Johnson County
- Radon levels in Cedar CountyEPA zone 1
60.4%at or above 4 pCi/L
Median 5.0 pCi/L · 765 tests · 18.8 points above Johnson County
- Radon levels in Iowa CountyEPA zone 1
59.2%at or above 4 pCi/L
Median 5.1 pCi/L · 519 tests · 17.6 points above Johnson County
- Radon levels in Washington CountyEPA zone 1
54.9%at or above 4 pCi/L
Median 4.6 pCi/L · 1,186 tests · 13.3 points above Johnson County
- Radon levels in Louisa CountyEPA zone 1
52.1%at or above 4 pCi/L
Median 4.1 pCi/L · 96 tests · 10.5 points above Johnson County
- Radon levels in Muscatine CountyEPA zone 1
46.5%at or above 4 pCi/L
Median 3.7 pCi/L · 954 tests · 4.9 points above Johnson County
- Radon levels in Linn CountyEPA zone 1
39.7%at or above 4 pCi/L
Median 3.0 pCi/L · 9,395 tests · 1.9 points below Johnson County
Johnson County, Cities and towns
Cities and towns in Johnson County
The Census Bureau estimates 160,044 residents in Johnson County for July 1, 2025, 6,973 more than in 2020 (+4.6%). That works out to 261 people per square mile of land. Its largest town, Iowa City, has 76,229 residents, 47.6% of the total. Testing is reported here more often than across the state: CDC's 7,321 reported tests for 2008 to 2017 come to 45.7 for every 1,000 residents (2025 estimate), against 29.4 for Iowa.
From Iowa City to Oxford, CDC publishes no figure by town: each reads Johnson County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Iowa City | 76,229 | +1.7% | 47.6% |
| Coralville | 23,960 | +7.3% | 15.0% |
| North Liberty | 21,976 | +7.2% | 13.7% |
| Tiffin | 7,156 | +54.7% | 4.5% |
| Solon | 3,345 | +10.0% | 2.1% |
| West Branchextends beyond Johnson County | 2,956 | +17.8% | Counted whole |
| Lone Tree | 1,332 | −1.3% | 0.8% |
| University Heights | 1,177 | −3.8% | 0.7% |
| Hills | 913 | +5.4% | 0.6% |
| Swisher | 901 | −1.9% | 0.6% |
| Shueyville | 722 | −1.1% | 0.5% |
| Oxford | 707 | −1.3% | 0.4% |
Places in Johnson County with a city page: 1 of 1
12 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). A place that extends beyond Johnson County is counted whole, so it has no share.
Johnson County, Homes
Homes in Johnson County
Fewer than six in ten of Johnson County's 67,211 homes are detached houses (49%, against 72% across Iowa); the rest are attached, in shared buildings or mobile. Much of Johnson County is recent building: 36% of its homes have gone up since 2000 and the middle year built is 1991, against 1971 for Iowa. 59% 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 | Johnson County | Iowa |
|---|---|---|
| Housing units | 67,211 | 1,427,175 |
| Detached houses | 49% | 72% |
| In buildings of 5 or more | 30% | 14% |
| Mobile homes | 4% | 3% |
| Built before 1960 | 17% | 39% |
| Built since 2000 | 36% | 21% |
| Middle year built | 1991 | 1971 |
| Owner-occupied | 59% | 72% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.