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, Indiana
EPA puts Johnson County in Zone 1, its highest radon zone, and 39.4% of its 556 reported radon tests (2008 to 2017, laboratory totals) were 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
39.4%
0.5 pts above IN
- Johnson
- 39.4%
- Indiana
- 38.9%
556 tests, 2008 to 2017
Median result
2.9pCi/L
Below action level
- Johnson
- 2.9 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2008 to 2017
Tests reported
556
17th of 69 by tests
- Johnson
- 556
- St. Joseph
- 7,346
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 Indiana
45 of 69
Middle half
- Johnson
- 39.4%
- Miami
- 63.3%
By share, of 69 with 30+ tests
Read a result for Johnson County
Starts at Johnson County's median, 2.9 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 2.9 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 99% 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: 39%2 to 4 pCi/L: 22%4 pCi/L and above: 39%
Of 556 pre-mitigation tests reported to CDC, not homes in this area.
| Result band | Tests Measured | Share Measured |
|---|---|---|
| Under 2 pCi/L | 218 | 39.2% |
| 2 to 4 pCi/L | 119 | 21.4% |
| 4 pCi/L and above | 219 | 39.4% |
What these figures count
These are the 556 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 (219 of 556) were at or above EPA's action level. Against the national pool of 35.7%, the gap is 3.7 points higher. Across 92 Indiana counties pooled together, 38.9% of tests reached that level, so Johnson County runs 0.5 points above its state.
Of 5 neighbours with a figure, 4 reported a larger share at or above 4 pCi/L and 1 a smaller one; the spread is 25.9% (Brown County) to 50.0% (Shelby County). By share, Johnson County is 45th of 69 Indiana counties with 30 or more tests for the same period.
Half the tests came in under 2.9 pCi/L and half over it; the single highest reached 81.6 pCi/L. Below the action level, 218 tests (39.2%) came in under 2 pCi/L, against 32.8% statewide, and 119 tests (21.4%) fell between 2 and 4, against 28.3% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 39.4% share point the same way here. USGS geology rates 99% of the county's land high radon potential. CDC also counts 99 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 457 tests (2005 to 2014) to 556 (2008 to 2017), the share going from 38.9% to 39.4%.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Johnson County, Geology
The ground under Johnson County
PredictedMost of the ground under Johnson County is one class on USGS's geologic map: 99.1% of its land is high radon potential, with 0.9% moderate. 99.1% of it lies in the area the map calls Huron-Erie Lobe, 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 |
|---|---|---|---|---|
| Huron-Erie Lobe | Calcareous clayey and loamy glacial deposits derived from marine carbonate and clastic sedimentary rocks. | High | 13 | 99.1% |
| Crawford Upland/Mitchell Plain/Norman Upland | Unglaciated, underlain by karsted Mississippian carbonate rocks. | Moderate | 11 | 0.9% |
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
Johnson County has more high-potential ground than Indiana as a whole: 99.1% of its land against 56.6%. Of the 5 counties that border it, 2 have more high-potential ground, Marion County the most 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
- Indiana's radon programIndiana Department of HealthIndiana's radon program licenses or certifies radon professionals and offers free or discounted test kits, and answers questions about testing and mitigation in Indiana.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
To purchase a low-cost radon short term or long term test kit, please visit the American Lung Association
- Compare kits
- Professionals in Indiana17 professionals are listed in Indiana.
What Indiana's program says
- Phone
- 1-800-272-9723
- Licensing of radon professionals
According to the Indiana Radon Rule, 410 IAC 5.1, everyone who is serving Indiana by doing radon testing, analysis and mitigation (radon reduction) in residential structures must be certified by the Indiana State Department of Health.
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, 39.4% of the radon tests reported to CDC for Johnson County, Indiana were at or above 4 pCi/L, and the median reported pre-mitigation result was 2.9 pCi/L. Of 69 Indiana counties with 30 or more tests for the same period, 44 reported a higher share; pooled, the state comes to 38.9%.
Which counties border Johnson County?
Johnson County borders 5 counties: Shelby County, Marion County, Morgan County, Bartholomew County and Brown County.
Products
Johnson County, Products
Testing a home in Johnson County
In Johnson County, 39.4% of 556 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 38.9% pooled across Indiana. 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
Monitor
Wave Plus battery radon and air quality monitor
- C-NRPP 2024/25: Not included
- Battery
- Bluetooth
- App only
Method: Alpha spectrometry
Short-term kitempowerDX
Standard Radon Test short-term mail-in radon test kit
- Lab fee included
Method: Passive sampler
In home: 48 to 96 hours
- 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 Shelby CountyEPA zone 1
50.0%at or above 4 pCi/L
Median 4.0 pCi/L · 84 tests · 10.6 points above Johnson County
- Radon levels in Bartholomew CountyEPA zone 1
48.7%at or above 4 pCi/L
Median 3.9 pCi/L · 1,707 tests · 9.3 points above Johnson County
- Radon levels in Morgan CountyEPA zone 2
44.2%at or above 4 pCi/L
Median 3.5 pCi/L · 226 tests · 4.8 points above Johnson County
- Radon levels in Marion CountyEPA zone 1
40.1%at or above 4 pCi/L
Median 3.1 pCi/L · 3,668 tests · 0.7 points above Johnson County
- Radon levels in Brown CountyEPA zone 2
25.9%at or above 4 pCi/L
Median 2.8 pCi/L · 112 tests · 13.5 points below Johnson County
Johnson County, Cities and towns
Cities and towns in Johnson County
Johnson County is growing: the Census Bureau puts it at 174,262 residents on July 1, 2025, up 7.4% from 162,237 in 2020. That works out to 544 people per square mile of land. Its largest town, Greenwood, has 69,349 residents, 39.8% of the total. Reported testing is thin here: 556 tests over 2008 to 2017, or 3.2 for every 1,000 residents (2025 estimate), where Indiana as a whole comes to 6.2.
From Greenwood to Prince's Lakes, CDC publishes no figure by town: each reads Johnson County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Greenwood | 69,349 | +8.4% | 39.8% |
| Franklin | 26,743 | +5.4% | 15.3% |
| Bargersville | 11,862 | +22.1% | 6.8% |
| New Whiteland | 5,937 | +6.6% | 3.4% |
| Whiteland | 5,884 | +26.4% | 3.4% |
| Edinburghextends beyond Johnson County | 4,575 | +3.1% | Counted whole |
| Trafalgar | 1,658 | +15.6% | 1.0% |
| Prince's Lakes | 1,384 | +0.9% | 0.8% |
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). A place that extends beyond Johnson County is counted whole, so it has no share.
Johnson County, Homes
Homes in Johnson County
Johnson County is a place of houses on their own lots: 77% of its 64,800 homes are detached single-family houses, against 73% across Indiana. Much of Johnson County is recent building: 33% of its homes have gone up since 2000 and the middle year built is 1992, against 1976 for Indiana. 74% of occupied homes are lived in by their owner (Indiana: 70%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Johnson County | Indiana |
|---|---|---|
| Housing units | 64,800 | 2,953,344 |
| Detached houses | 77% | 73% |
| In buildings of 5 or more | 11% | 13% |
| Mobile homes | 2% | 4% |
| Built before 1960 | 15% | 32% |
| Built since 2000 | 33% | 21% |
| Middle year built | 1992 | 1976 |
| Owner-occupied | 74% | 70% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.