Madison County, Idaho
USDA's soil survey flags shrink-swell clay on under 1% of Madison County's mapped land and a shallow water table under basements on 14%, both below the national shares of 15% and 29%. 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. 28% of homes were built before 1980, against 50% nationally; the median home dates from 2002.
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 Madison County
| Expansive clay (limits slab homes) | 0.4% |
| High water table (limits basements) | 14.3% |
| Septic fields very limited | 53.7% |
| Clay swell (LEP, by area) | 2.2% |
| High-swell land (LEP 6%+) | 0.4% |
| Mapped soil | 356,562 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Ririe | 13% | n/a |
| Rexburg | 10% | n/a |
| Gany | 9% | n/a |
| Tetonia | 7% | n/a |
| Greys | 6% | n/a |
| Fritz | 5% | n/a |
How we count · survey areas ID758 (2025-08-27), ID766 (2025-08-27)
What the numbers mean here
Rain over the 12 months to August 2026: 14.42 in, 1.60 in below the 1991-2020 average year of 16.02 in.
USDA rates 54% of the land very limited for septic absorption fields.
With shrink-swell clay on under 1% and a shallow water table on 14% of the land, the soil survey points to neither problem across most of Madison County; conditions still vary lot by lot.
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 52 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 | 72.3% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in Madison County since 2016.
Rain
| Average year, 1991-2020 | 16.02 in |
| 12 months to August 2026 | 14.42 in (-1.60) |
| 2025 | 14.57 in (-1.45) |
| Wettest year since 1895 | 1983: 23.63 in |
| Driest year since 1895 | 1898: 9.32 in |
| Days with 1 inch or more, normal at SAINT ANTHONY (11 mi away) | 1 |
Homes
| Housing units | 15,145 |
| Median year built | 2002 |
| Built before 1980 | 28% |
| Built 2000 or later | 56% |
| Owner-occupied | 40% |
| Median value, owner-occupied | $414,800 |
| Single-family detached | 39% |
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 |
|---|---|---|---|
| Teton County, ID | 22 mi | 5% | 12% |
| Bonneville County, ID | 27 mi | 11% | 4% |
| Fremont County, ID | 31 mi | 1% | 6% |
| Jefferson County, ID | 33 mi | 21% | 8% |
| Clark County, ID | 49 mi | 4% | 4% |
| Bingham County, ID | 54 mi | under 1% | 2% |
| Teton County, WY | 64 mi | 7% | 6% |
| Caribou County, ID | 70 mi | 13% | 4% |
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