Johnson County, Kansas
Shrink-swell clay limits houses without basements on 73% of Johnson County's mapped land, a higher share than 98% of US counties. A shallow water table limits basements on 65%.
None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 146 flood losses here since 2016, 60% of them in buildings with basements. 36% of homes were built before 1980, against 50% nationally; the median home dates from 1989.
Data as of October 13, 2026 · sources
expansive clay: shrink-swell limits slab homes
high water table: limits basements
in drought, October 13, 2026
of homes built before 1980
Soil under Johnson County
| Expansive clay (limits slab homes) | 73.1% |
| High water table (limits basements) | 64.8% |
| Septic fields very limited | 93.9% |
| Clay swell (LEP, by area) | 7.3% |
| High-swell land (LEP 6%+) | 72.5% |
| Urban land, not rated | 3.2% |
| Mapped soil | 307,066 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Chillicothe | 15% | n/a |
| Woodson | 14% | n/a |
| Oska | 10% | n/a |
| Martin | 8% | n/a |
| Sharpsburg | 6% | 98% |
| Grundy | 5% | n/a |
How we count · survey areas KS091 (2025-08-26)
What the numbers mean here
Clay swell averages a linear extensibility of 7.3% by land area here, and 73% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 73% of the mapped land.
On 65% of Johnson County's mapped land, soil stays saturated within about 6 feet of the surface for part of the year, which is basement depth.
Rain over the 12 months to August 2026: 35.98 in, 3.57 in below the 1991-2020 average year of 39.55 in.
USDA rates 94% of the land very limited for septic absorption fields.
Drought
0% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 12 of the last 52 weeks; the most was 100% of its area, in 12 weeks, most recently on the January 6, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 0% |
| D1 moderate drought or worse | 0% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
146 flood losses since 2016, $3.9 million paid. The worst year was 2017, with 100. Foundations of the buildings, where recorded: 60% basements, 29% slabs, 10% elevated. Median water depth outside the building: 9 in.
| Year | Flood losses |
|---|---|
| 2016 | 10 |
| 2017 | 100 |
| 2018 | 2 |
| 2019 | 4 |
| 2020 | 3 |
| 2021 | 2 |
| 2022 | 1 |
| 2023 | 0 |
| 2024 | 11 |
| 2025 | 13 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 39.55 in |
| 12 months to August 2026 | 35.98 in (-3.57) |
| 2025 | 31.20 in (-8.35) |
| Wettest year since 1895 | 1973: 60.99 in |
| Driest year since 1895 | 1936: 21.44 in |
| Days with 1 inch or more, normal at BONNER SPRINGS (13 mi away) | 11.6 |
Homes
| Housing units | 259,655 |
| Median year built | 1989 |
| Built before 1980 | 36% |
| Built 2000 or later | 31% |
| Owner-occupied | 69% |
| Median value, owner-occupied | $391,200 |
| Single-family detached | 66% |
What repairs cost
Published ranges from cost guides, not quotes. More sources, and where they disagree.
Nearby counties
| Place | Distance | Expansive clay | High water table |
|---|---|---|---|
| Wyandotte County, KS | 16 mi | 61% | 28% |
| Miami County, KS | 22 mi | 83% | 67% |
| Leavenworth County, KS | 24 mi | 63% | 52% |
| Douglas County, KS | 25 mi | 56% | 51% |
| Jackson County, MO | 27 mi | 36% | 50% |
| Cass County, MO | 30 mi | 68% | 80% |
| Franklin County, KS | 33 mi | 75% | 70% |
| Platte County, MO | 34 mi | 30% | 57% |
Sources: USDA SSURGO (August 26, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status