Franklin County, Idaho
Shrink-swell clay limits houses without basements on 21% of Franklin County's mapped land, a higher share than 71% of US counties and the 6th highest of 43 Idaho counties. A shallow water table limits basements on 8%.
The soil survey maps 87% of the county's land area; these shares describe the mapped part. 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. 56% of homes were built before 1980, against 50% nationally; the median home dates from 1975.
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 Franklin County
| Expansive clay (limits slab homes) | 20.8% |
| High water table (limits basements) | 8.2% |
| Septic fields very limited | 91.9% |
| Clay swell (LEP, by area) | 3.8% |
| High-swell land (LEP 6%+) | 22.0% |
| Mapped soil | 367,929 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Manila | 4% | n/a |
| Oxford | 3% | n/a |
| Broad Canyon | 3% | n/a |
| Parleys | 3% | n/a |
| Banida | 3% | n/a |
| Kidman | 3% | n/a |
How we count · survey areas ID713 (2025-08-27), ID714 (2025-08-27)
What the numbers mean here
Clay swell averages a linear extensibility of 3.8% by land area here, and 22% 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 Franklin County's mapped land has shrink-swell clay.
Rain over the 12 months to August 2026: 21.06 in, 2.06 in below the 1991-2020 average year of 23.12 in.
USDA rates 92% 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 39 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 | 87.2% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in Franklin County since 2016.
Rain
| Average year, 1991-2020 | 23.12 in |
| 12 months to August 2026 | 21.06 in (-2.06) |
| 2025 | 21.61 in (-1.51) |
| Wettest year since 1895 | 1983: 38.34 in |
| Driest year since 1895 | 1966: 14.18 in |
| Days with 1 inch or more, normal at PRESTON (6 mi away) | 1.2 |
Homes
| Housing units | 5,212 |
| Median year built | 1975 |
| Built before 1980 | 56% |
| Built 2000 or later | 27% |
| Owner-occupied | 78% |
| Median value, owner-occupied | $372,600 |
| Single-family detached | 88% |
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 |
|---|---|---|---|
| Bear Lake County, ID | 27 mi | 6% | 16% |
| Cache County, UT | 31 mi | 22% | 18% |
| Oneida County, ID | 36 mi | 5% | 4% |
| Bannock County, ID | 41 mi | n/a | n/a |
| Caribou County, ID | 44 mi | 13% | 4% |
| Rich County, UT | 48 mi | 1% | 7% |
| Lincoln County, WY | 58 mi | 19% | 5% |
| Weber County, UT | 62 mi | 7% | 20% |
Sources: USDA SSURGO (August 27, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status