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
Locations and reports
Radon Levels in Riley County, Kansas
EPA puts Riley County in Zone 1, its highest radon zone, and 31.3% of its 800 reported radon tests (2022) 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
31.3%
0.7 pts below KS
- Riley
- 31.3%
- Kansas
- 32.0%
800 tests, 2022
Median result
1.9pCi/L
Below action level
- Riley
- 1.9 pCi/L
- EPA
- 4.0 pCi/L
Midpoint of the tests, 2022
Tests reported
800
4th of 38 by tests
- Riley
- 800
- Johnson
- 5,240
Reported to CDC before any fix, 2022
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
22 of 38
Middle half
- Riley
- 31.3%
- Mitchell
- 57.4%
By share, of 38 with 30+ tests
Read a result for Riley County
Starts at Riley County's median, 1.9 pCi/L
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 1.9 pCi/L
Below 2 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is below 2 pCi/L, the level at which EPA says a fix should be considered. Riley County's median reported result, 2022.
The data
Riley County, At a glance
Riley County at a glance
Predicted: EPA radon zone
EPA Zone 1: highest predicted potential
EPA puts all of Riley 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 Riley County, 2022
| Year | Share of reported tests at or above 4 pCi/L |
|---|---|
| 2016 | 26.1% |
| 2017 | 31.2% |
| 2018 | 28.9% |
| 2019 | 27.9% |
| 2020 | 27.8% |
| 2021 | 33.9% |
| 2022 | 31.3% |
2022: 31.3%. Across these years the share ran from 26.1% to 33.9%. Each column counts radon tests reported to CDC that year, not homes.
What these figures count
These are the 800 tests reported to CDC for Riley County over 2022, 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: 2022. Measured data period: 2016 to 2022 (every CDC figure on file).
Riley County, Compared
Riley County radon figures, compared
Calculated by Radon411In Riley County, about 3 in 10 reported tests in 2022 (250 of 800) were at or above EPA's action level. Against the national pool of 23.9%, the gap is 7.4 points higher. Across 96 Kansas counties pooled together, 32.0% of tests reached that level, so Riley County runs 0.7 points below its state.
Of 5 neighbours with a figure, 2 reported a larger share at or above 4 pCi/L and 3 a smaller one; the spread is 25.2% (Pottawatomie County) to 55.8% (Clay County). By share, Riley County is 22nd of 38 Kansas counties with 30 or more tests for the same period.
Year by year, 2016 opened at 26.1% and 2022 closed at 31.3% (up 5.2 points), with 2021 the high at 33.9%. Half the tests came in under 1.9 pCi/L and half over it; the single highest reached 28.2 pCi/L. Below the action level, 400 tests (50.0%) came in under 2 pCi/L, against 45.8% statewide, and 150 tests (18.8%) fell between 2 and 4, against 22.1% statewide.
Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 31.3% share point the same way here. USGS geology rates 100% of the county's land high radon potential. CDC also counts 82 tests taken after mitigation in Riley County for the same period: tests in homes where a fix was already in.
The busiest year on file was 2021, with 3,132 tests reported; the quietest, 2016, had 667.
Riley CountyKansas, pooled
| Year | Tests | Riley County, at or above 4 pCi/L | Kansas, pooled |
|---|---|---|---|
| 2016 | 667 | 26.1% | 35.4% |
| 2017 | 836 | 31.2% | 37.3% |
| 2018 | 984 | 28.9% | 37.3% |
| 2019 | 707 | 27.9% | 33.7% |
| 2020 | 992 | 27.8% | 31.3% |
| 2021 | 3,132 | 33.9% | 31.8% |
| 2022 | 800 | 31.3% | 32.0% |
Pooled shares: Radon411's sum of CDC's county counts for one period.
Riley County, Geology
The ground under Riley County
PredictedUSGS's geologic map puts all of Riley County's mapped land in one class: high radon potential. The map puts 93.8% of Riley County in the area it calls Mid-Continent Rift Zone and 6.2% in Glacial Drift. USGS gives both 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 |
|---|---|---|---|---|
| Mid-Continent Rift Zone | Faulted and fractured Permian limestone, dolomite, shale, and sandstone related to the Mid-Continent Rift zone. | High | 12 | 93.8% |
| Glacial Drift | Glacial drift and loess of varying thickness, largely locally derived from underlying and nearby Paleozoic sedimentary rocks. | High | 12 | 6.2% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Riley County beside the ground around it
Riley 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; Marshall County comes nearest at 99.6%.
The map rates the ground, not the air in any home.
Local help
Riley County, Local resources
Radon testing and mitigation in Riley County
Listed radon businesses with an address in Riley 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: Manhattan
What Kansas's program says
- Phone
- (800) 693-5343
What it means
Riley County, Questions
Questions about radon in Riley County
Are radon levels high in Riley County?
In 2022, 31.3% of the radon tests reported to CDC for Riley County, Kansas were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.9 pCi/L. Of 38 Kansas counties with 30 or more tests for the same period, 21 reported a higher share; pooled, the state comes to 32.0%.
Which counties border Riley County?
Riley County borders 6 counties: Geary County, Clay County, Pottawatomie County, Marshall County, Washington County and Wabaunsee County.
Products
Riley County, Products
Testing a home in Riley County
In Riley County, 31.3% of 800 tests reported to CDC in 2022 reached 4 pCi/L, against 32.0% pooled across Kansas. In Zone 1 the year-round level in Riley 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
MonitorX-Sense
XR0A-SR battery digital radon detector with a screen
- C-NRPP 2024/25: Not included
- Battery
- Screen
Method: Alpha spectrometry
First reading: Within 24 hours
Short-term kit
RA100 short-term liquid scintillation radon test kit
- Lab fee extra
Method: Liquid scintillation
In home: 48 to 96 hours
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Riley County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Riley County
Explore
Riley County, Bordering counties
Counties bordering Riley County
Calculated by Radon411- Radon levels in Clay CountyEPA zone 1
55.8%at or above 4 pCi/L
Median 4.8 pCi/L · 77 tests · 24.5 points above Riley County
- Radon levels in Washington CountyEPA zone 1
43.8%at or above 4 pCi/L
Median 3.3 pCi/L · 16 tests · 12.5 points above Riley County
- Radon levels in Marshall CountyEPA zone 1
31.8%at or above 4 pCi/L
Median 1.9 pCi/L · 66 tests · 0.5 points above Riley County
- Radon levels in Wabaunsee CountyEPA zone 2
29.0%at or above 4 pCi/L
Median 2.2 pCi/L · 31 tests · 2.3 points below Riley County
- Radon levels in Geary CountyEPA zone 1
25.2%at or above 4 pCi/L
Median 1.9 pCi/L · 365 tests · 6.1 points below Riley County
- Radon levels in Pottawatomie CountyEPA zone 1
25.2%at or above 4 pCi/L
Median 1.7 pCi/L · 206 tests · 6.1 points below Riley County
Riley County, Cities and towns
Cities and towns in Riley County
The Census Bureau estimates 72,598 residents in Riley County for July 1, 2025, 587 more than in 2020 (+0.8%). That works out to 119 people per square mile of land. Manhattan, the largest place on its list (54,673 residents in all), extends beyond Riley County, so no share of the total is worked out for it. Testing is reported here more often than across the state: CDC's 800 reported tests for 2022 come to 11.0 for every 1,000 residents (2025 estimate), against 6.2 for Kansas.
From Manhattan to Randolph, CDC publishes no figure by town: each reads Riley County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Manhattanextends beyond Riley County | 54,673 | +1.0% | Counted whole |
| Ogden | 1,655 | −0.7% | 2.3% |
| Riley | 956 | +1.6% | 1.3% |
| Leonardville | 442 | +2.6% | 0.6% |
| Randolph | 159 | −0.6% | 0.2% |
Places in Riley County with a city page: 1 of 1
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). A place that extends beyond Riley County is counted whole, so it has no share.
Riley County, Homes
Homes in Riley County
Fewer than six in ten of Riley County's 30,674 homes are detached houses (48%, against 72% across Kansas); the rest are attached, in shared buildings or mobile. Much of Riley County is recent building: 31% of its homes have gone up since 2000 and the middle year built is 1984, against 1975 for Kansas. Most occupied homes here are rented: owners live in 45% (Kansas: 67%). A tenant can run a test; a fix is the landlord's to make.
| Homes | Riley County | Kansas |
|---|---|---|
| Housing units | 30,674 | 1,285,221 |
| Detached houses | 48% | 72% |
| In buildings of 5 or more | 26% | 13% |
| Mobile homes | 5% | 4% |
| Built before 1960 | 22% | 33% |
| Built since 2000 | 31% | 20% |
| Middle year built | 1984 | 1975 |
| Owner-occupied | 45% | 67% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.