Johnston County, Oklahoma
Shrink-swell clay limits houses without basements on 21% of Johnston County's mapped land, a higher share than 71% of US counties. A shallow water table limits basements on 19%.
100% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list no flood losses here since 2016. 45% of homes were built before 1980, against 50% nationally; the median home dates from 1983.
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 Johnston County
| Expansive clay (limits slab homes) | 20.6% |
| High water table (limits basements) | 19.1% |
| Septic fields very limited | 70.1% |
| Clay swell (LEP, by area) | 4.7% |
| High-swell land (LEP 6%+) | 20.6% |
| Mapped soil | 421,184 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Gasil | 16% | 0% |
| Chigley | 9% | n/a |
| Claremore | 8% | n/a |
| Kiti | 6% | n/a |
| Lula | 5% | n/a |
| Agan | 5% | n/a |
How we count · survey areas OK069 (2025-08-29)
What the numbers mean here
Clay swell averages a linear extensibility of 4.7% by land area here, and 21% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 21% of the mapped land.
Clay shrinks as it dries: 100% of the county is in drought on the latest map, and 21% of Johnston County's mapped land has shrink-swell clay.
On 19% of Johnston 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, 6.64 in below the 1991-2020 average year of 42.62 in.
USDA rates 70% of the land very limited for septic absorption fields.
Drought
100% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 52 of the last 52 weeks; the most was 100% of its area, in 31 weeks, most recently on the October 13, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 100% |
| D2 severe or worse | 90% |
| D3 extreme or worse | 7% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in Johnston County since 2016.
Rain
| Average year, 1991-2020 | 42.62 in |
| 12 months to August 2026 | 35.98 in (-6.64) |
| 2025 | 46.97 in (+4.35) |
| Wettest year since 1895 | 2015: 76.68 in |
| Driest year since 1895 | 1963: 18.77 in |
| Days with 1 inch or more, normal at TISHOMINGO NATL WR (7 mi away) | 14 |
Homes
| Housing units | 4,708 |
| Median year built | 1983 |
| Built before 1980 | 45% |
| Built 2000 or later | 27% |
| Owner-occupied | 72% |
| Median value, owner-occupied | $116,500 |
| Single-family detached | 75% |
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 |
|---|---|---|---|
| Marshall County, OK | 21 mi | 30% | 1% |
| Murray County, OK | 27 mi | 29% | 7% |
| Coal County, OK | 28 mi | 54% | 71% |
| Pontotoc County, OK | 28 mi | 28% | 15% |
| Bryan County, OK | 33 mi | 42% | 19% |
| Atoka County, OK | 36 mi | 45% | 36% |
| Carter County, OK | 36 mi | 23% | 3% |
| Love County, OK | 42 mi | 17% | 2% |
Sources: USDA SSURGO (August 29, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status