Short-term kit
RA400 short-term liquid scintillation radon test kit, lab fee included
- Lab fee included
Method: Liquid scintillation
In home: 48 to 96 hours
Locations and reports
Radon Levels in Johnson County, Arkansas
EPA puts Johnson County in Zone 3, its lowest radon zone, and only 3 radon tests from it are on file with CDC (2008 to 2017, laboratory totals). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Nearest county
14.3%
Washington County, 51 miles
- Washington
- 14.3%
- Arkansas
- 22.7%
Share at 4+ pCi/L, 56 tests, 2007 to 2016
Ground above low
None
21.3 pts below Arkansas
- Johnson
- 0.0%
- Arkansas
- 21.3%
Share of land USGS rates moderate or high potential
Tests reported
3
Too few for a share
- Johnson
- 3
- Needed
- 30
2008 to 2017, laboratory
EPA radon zone
Zone 3
Lower potential
- 1
- 2
- Zone 3
1 highest, 3 lowest
EPA predicts under 2 pCi/L indoors
Read a result for Johnson County
Starts at EPA's action level
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 4.0 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.
The data
Johnson County, At a glance
Johnson County at a glance
Predicted: EPA radon zone
EPA Zone 3: lower predicted potential
USGS geologic potential: Low 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
CDC holds 3 reported tests for Johnson County over the 2008 to 2017 laboratory totals, with a median of 9.7 pCi/L: too few to describe a county (Radon411 reads a share from 30 tests up). Johnson County beside the counties around it is how this page reads it.
What these figures count
Only 3 tests were reported to CDC for Johnson County over 2008 to 2017 (laboratory totals), and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor 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 Radon411CDC's largest figure for Johnson County rests on 3 tests over the 2008 to 2017 laboratory totals, 2 of them at or above 4 pCi/L, so each test moves its share by 33.3 points and no rank or comparison is drawn from it. Results reached as high as 11.8 pCi/L, with a middle value of 9.7 pCi/L.
The nearest counties with a figure are Washington County (51 miles away) at 14.3%, Benton County (69 miles away) at 31.0% and Garland County (71 miles away) at 45.8%. Pooled across 60 Arkansas counties, 22.7% of reported tests reached that level; across every county in the country with a figure, 35.8%.
Statewide for the same period, Garland County reported the highest share (45.8%) and Pulaski County the lowest (6.8%). EPA's 1993 map puts Johnson County in Zone 3, its lowest label: a predicted county average under 2 pCi/L. USGS geology rates 100% of the county's land low radon potential.
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: low radon potential. The map puts 63.1% of Johnson County in the area it calls Boston Mountains and 36.9% in Arkansas Valley. USGS gives both a radon index of 8, in the low band (5 to 8).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Boston Mountains | Mississippian and Pennsylvanian sandstones and shales. | Low | 8 | 63.1% |
| Arkansas Valley | Mississippian and Pennsylvanian sandstones and shales. | Low | 8 | 36.9% |
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
Across Arkansas 21.3% of the land is rated moderate; none of Johnson County's is. Of the 5 counties that border it, 2 have more moderate-potential ground, Newton County the most at 48.8%.
The map rates the ground, not the air in any home.
Local help
Johnson County, Local resources
Radon testing and mitigation in Johnson County
- Arkansas's radon programArkansas Department of HealthArkansas's radon program answers questions about testing, mitigation and the rules in Arkansas.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsAsk the program whether it has free or discounted kits, or compare kits you can buy.
- Compare kits
- See the Arkansas directoryNo professionals are listed in Arkansas yet. The state program can point you to registered testers and mitigators.
What Arkansas's program says
- Phone
- 501-661-2621
- ADH.EPI.Radon@arkansas.gov
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, 66.7% of the radon tests reported to CDC for Johnson County, Arkansas were at or above 4 pCi/L, and the median reported pre-mitigation result was 9.7 pCi/L. Of the 5 nearest counties with a figure, within 85 miles, the share of tests at or above 4 pCi/L runs from 6.8% to 45.8%.
Which counties border Johnson County?
Johnson County borders 5 counties: Franklin County, Pope County, Logan County, Newton County and Madison County.
Products
Johnson County, Products
Testing a home in Johnson County
No CDC figure names Johnson County; the nearest county with one, Washington County (51 miles away), reported 14.3% of its tests at or above 4 pCi/L over the 2007 to 2016 laboratory totals, the only reading nearby until a test of this home. Zone 3 is the lowest label, yet homes at or above 4 pCi/L occur in every zone: a short-term kit (2 to 90 days) is the quick first check in Johnson County.
Test kits and monitors3
See every kit and monitor
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
MonitorAEGTEST
HOUND-3786 rechargeable radon monitor with a 3.5-inch color screen
- C-NRPP 2024/25: Not included
- Battery
- Alarm
- Screen
Method: Ion chamber
First reading: Within 10 minutes
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Johnson County, Bordering counties
Counties bordering Johnson County
Calculated by Radon411- Radon levels in Logan CountyEPA zone 3
20.0%at or above 4 pCi/L
Median 2.1 pCi/L · 5 tests
- Radon levels in Madison CountyEPA zone 3
16.7%at or above 4 pCi/L
Median 1.0 pCi/L · 6 tests
- Radon levels in Pope CountyEPA zone 3
15.4%at or above 4 pCi/L
Median 2.7 pCi/L · 13 tests
- Radon levels in Franklin CountyEPA zone 3
0.0%at or above 4 pCi/L
Median 0.1 pCi/L · 1 test
- Radon levels in Newton CountyEPA zone 3
0.0%at or above 4 pCi/L
Median 3.0 pCi/L · 1 test
Johnson County, Cities and towns
Cities and towns in Johnson County
The Census Bureau estimates 26,225 residents in Johnson County for July 1, 2025, 504 more than in 2020 (+2.0%). That works out to 40 people per square mile of land. Its largest town, Clarksville, has 9,632 residents, 36.7% of the total. Together its 5 incorporated places hold 51.1% of those residents; the other 48.9% live outside any of them. Reported testing is thin here: 3 tests over 2008 to 2017, or 0.1 for every 1,000 residents (2025 estimate), where Arkansas as a whole comes to 0.2.
From Clarksville to Hartman, CDC publishes no figure by town: each reads Johnson County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Clarksville | 9,632 | +2.9% | 36.7% |
| Lamar | 1,776 | +3.3% | 6.8% |
| Coal Hill | 822 | +1.1% | 3.1% |
| Knoxville | 662 | +1.7% | 2.5% |
| Hartman | 518 | +0.8% | 2.0% |
5 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).
Johnson County, Homes
Homes in Johnson County
Johnson County is a place of houses on their own lots: 76% of its 11,523 homes are detached single-family houses, against 70% across Arkansas. Half of its homes were built before 1985, close to Arkansas' 1987: 18% date from before 1960 and 20% from 2000 or later. 72% of occupied homes are lived in by their owner (Arkansas: 66%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Johnson County | Arkansas |
|---|---|---|
| Housing units | 11,523 | 1,382,664 |
| Detached houses | 76% | 70% |
| In buildings of 5 or more | 3% | 10% |
| Mobile homes | 11% | 11% |
| Built before 1960 | 18% | 14% |
| Built since 2000 | 20% | 28% |
| Middle year built | 1985 | 1987 |
| Owner-occupied | 72% | 66% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.