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 Thomas County, Kansas
EPA puts Thomas County in Zone 1, its highest radon zone, and only 23 radon tests from it are on file with CDC (2022). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Share at 4+ pCi/L
54.7%
17.4 pts above KS
- Thomas
- 54.7%
- Kansas
- 37.3%
64 tests, 2017
Median result
4.3pCi/L
Action level reached
- Thomas
- 4.3 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2017
Tests reported
64
29th of 45 by tests
- Thomas
- 64
- Johnson
- 9,462
Reported to CDC before any fix, 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 Kansas
9 of 45
Top quarter
- Thomas
- 54.7%
- Sheridan
- 67.7%
By share, of 45 with 30+ tests
Read a result for Thomas County
Starts at Thomas County's median, 4.3 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 4.3 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. Thomas County's median reported result, 2017.
The data
Thomas County, At a glance
Thomas County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Thomas 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 Thomas County, 2022
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2016 | 67.7% |
| 2017 | 54.7% |
| 2018 | 63.0% |
| 2019 | 45.5% |
| 2020 | 65.5% |
| 2021 | 56.3% |
| 2022 | 56.5% |
2022: 56.5%. Across these years the share ran from 45.5% to 67.7%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
Only 23 tests were reported to CDC for Thomas County over 2022, 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: 2022. Measured data period: 2016 to 2022 (every CDC figure on file).
Thomas County, Compared
Thomas County radon figures, compared
Calculated by Radon411More than half: 54.7% of the 64 radon tests reported to CDC for Thomas County in 2017 read at least 4 pCi/L. That places it 9th of 45 Kansas counties with 30 or more tests for the same period. That is 17.4 points above the 37.3% pooled from 97 Kansas counties.
The newest figure, in 2022, counts only 23 tests (56.5% at or above 4 pCi/L), too few to compare, so this reading uses the 64-test figure.
The median result, 4.3 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 17.5 pCi/L. The rest split 7.8% under 2 pCi/L and 37.5% from 2 to 4 (Kansas: 39.5% and 23.2%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 54.7% share point the same way here.
All 3 of its bordering counties with figures ran higher, led by Sheridan County at 67.7%; the lowest of them, Sherman County, reported 55.3%. Statewide for the same period, Sheridan County reported the highest share (67.7%) and Reno County the lowest (21.6%).
The busiest year on file was 2017, with 64 tests reported; the quietest, 2022, had 23.
Over 5 years of annual figures the share fell 11.4 points, from 67.7% in 2016 to 56.3% in 2021; its peak was 67.7% in 2016. Nationally, every county with a figure for the same period pools to 31.7%; Thomas County sits 23.0 points above it.
Thomas CountyKansas, pooled
56.3% % of tests31.8% % of tests
| Year | Tests | Thomas County, at or above 4 pCi/L | Kansas, pooled |
|---|---|---|---|
| 2016 | 31 | 67.7% | 35.4% |
| 2017 | 64 | 54.7% | 37.3% |
| 2018 | 54 | 63.0% | 37.3% |
| 2019 | 44 | 45.5% | 33.7% |
| 2021 | 48 | 56.3% | 31.8% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Thomas County, Geology
The ground under Thomas County
PredictedUSGS's geologic map puts all of Thomas County's mapped land in one class: high radon potential. All of it lies in the area the map calls Ogallala Formation, to which USGS gives a radon index of 12, in the high band (12 to 17).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Ogallala Formation | Tertiary sandstone, in part covered by windblown eolian sand and loess deposits. | High | 12 | 100% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Thomas County beside the ground around it
Thomas County has more high-potential ground than Kansas as a whole: 100% of its land against 59.9%. Of the 6 counties that border it, none has as large a share of high-potential ground; Decatur County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Thomas County, Local resources
Radon testing and mitigation in Thomas County
- Kansas Radon ProgramKansas Radon Program answers questions about testing, mitigation and the rules in Kansas.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
- Professionals in Kansas178 professionals are listed in Kansas.
Listed radon professionals by town: Oakley
What Kansas's program says
- Phone
- (800) 693-5343
What it means
Thomas County, Questions
Questions about radon in Thomas County
Are radon levels high in Thomas County?
In 2022, 56.5% of the radon tests reported to CDC for Thomas County, Kansas were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.2 pCi/L. Of 45 Kansas counties with 30 or more tests for the same period, 8 reported a higher share; pooled, the state comes to 37.3%.
Which counties border Thomas County?
Thomas County borders 6 counties: Rawlins County, Logan County, Sheridan County, Sherman County, Gove County and Decatur County.
Products
Thomas County, Products
Testing a home in Thomas County
In Thomas County, 54.7% of 64 tests reported to CDC in 2017 reached 4 pCi/L, against 37.3% pooled across Kansas. In Zone 1 the year-round level in Thomas 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
EcoQube Flex 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 15 minutes
Short-term kit
PicoCan short-term charcoal canister radon test
- Lab fee included
Method: Charcoal
In home: 48 to 96 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Thomas County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Thomas County
Explore
Thomas County, Bordering counties
Counties bordering Thomas County
Calculated by Radon411- Radon levels in Rawlins CountyEPA zone 1
71.4%at or above 4 pCi/L
Median 7.2 pCi/L · 7 tests · 16.7 points above Thomas County
- Radon levels in Sheridan CountyEPA zone 1
67.7%at or above 4 pCi/L
Median 5.8 pCi/L · 31 tests · 13.0 points above Thomas County
- Radon levels in Logan CountyEPA zone 1
65.9%at or above 4 pCi/L
Median 4.7 pCi/L · 41 tests · 11.2 points above Thomas County
- Radon levels in Gove CountyEPA zone 1
63.2%at or above 4 pCi/L
Median 7.0 pCi/L · 19 tests · 8.5 points above Thomas County
- Radon levels in Decatur CountyEPA zone 1
58.3%at or above 4 pCi/L
Median 4.4 pCi/L · 12 tests · 3.6 points above Thomas County
- Radon levels in Sherman CountyEPA zone 1
55.3%at or above 4 pCi/L
Median 4.2 pCi/L · 76 tests · 0.6 points above Thomas County
Thomas County, Cities and towns
Cities and towns in Thomas County
About 7,725 people live in Thomas County by the Census Bureau's estimate for July 1, 2025, 201 fewer than in 2020 (−2.5%). Spread over its land, that is 7.2 people to the square mile. Colby alone is home to 5,489 of them, 71.1% of the total. CDC's 64 reported tests for 2017 work out to 8.3 per 1,000 residents (2025 estimate), close to Kansas' 8.0.
From Colby to Menlo, CDC publishes no figure by town: each reads Thomas County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Colby | 5,489 | −2.1% | 71.1% |
| Oakleyextends beyond Thomas County | 1,974 | −2.9% | Counted whole |
| Brewster | 278 | −4.1% | 3.6% |
| Rexford | 192 | −3.5% | 2.5% |
| Gem | 93 | −3.1% | 1.2% |
| Menlo | 30 | −3.2% | 0.4% |
6 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 Thomas County is counted whole, so it has no share.
Thomas County, Homes
Homes in Thomas County
Thomas County is a place of houses on their own lots: 81% of its 3,580 homes are detached single-family houses, against 72% across Kansas. The homes are older than Kansas' as a whole: half were built before 1965 (1975 for Kansas), and 41% date from before 1960. Owners live in 77% of the occupied homes (Kansas: 67%), so for most households a test and a fix are their own to order.
| Homes | Thomas County | Kansas |
|---|---|---|
| Housing units | 3,580 | 1,285,221 |
| Detached houses | 81% | 72% |
| In buildings of 5 or more | 6% | 13% |
| Mobile homes | 6% | 4% |
| Built before 1960 | 41% | 33% |
| Built since 2000 | 4% | 20% |
| Middle year built | 1965 | 1975 |
| Owner-occupied | 77% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.