Granite County, Montana
USDA's soil survey flags shrink-swell clay on 6% of Granite County's mapped land and a shallow water table under basements on 7%, both below the national shares of 15% and 29%. None 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. 51% of homes were built before 1980, against 50% nationally; the median home dates from 1980.
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 Granite County
| Expansive clay (limits slab homes) | 5.7% |
| High water table (limits basements) | 7.3% |
| Septic fields very limited | 86.0% |
| Clay swell (LEP, by area) | 2.4% |
| High-swell land (LEP 6%+) | 5.7% |
| Mapped soil | 1,084,289 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Whitecow | 3% | n/a |
| Danvers | 2% | n/a |
| Braziel | 2% | n/a |
| Yreka | 2% | n/a |
| Roy | 2% | n/a |
| Worock | 2% | n/a |
How we count · survey areas MT603 (2025-09-02), MT621 (2025-08-30), MT635 (2025-08-31)
What the numbers mean here
Rain over the 12 months to August 2026: 27.13 in, 3.27 in above the 1991-2020 average year of 23.86 in.
USDA rates 86% of the land very limited for septic absorption fields.
With shrink-swell clay on 6% and a shallow water table on 7% of the land, the soil survey points to neither problem across most of Granite County; conditions still vary lot by lot.
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 13 of the last 52 weeks; the most was 100% of its area, in 10 weeks, most recently on the December 23, 2025 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
FEMA's flood data list no flood losses in Granite County since 2016.
Rain
| Average year, 1991-2020 | 23.86 in |
| 12 months to August 2026 | 27.13 in (+3.27) |
| 2025 | 25.05 in (+1.19) |
| Wettest year since 1895 | 1975: 39.63 in |
| Driest year since 1895 | 1935: 13.25 in |
| Days with 1 inch or more, normal at DRUMMOND AVIATION (21 mi away) | 0.4 |
Homes
| Housing units | 2,602 |
| Median year built | 1980 |
| Built before 1980 | 51% |
| Built 2000 or later | 34% |
| Owner-occupied | 78% |
| Median value, owner-occupied | $352,700 |
| Single-family detached | 84% |
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 |
|---|---|---|---|
| Deer Lodge County, MT | 25 mi | 6% | 10% |
| Powell County, MT | 39 mi | 10% | 6% |
| Ravalli County, MT | 39 mi | under 1% | 8% |
| Missoula County, MT | 49 mi | 1% | 3% |
| Silver Bow County, MT | 50 mi | 2% | 5% |
| Jefferson County, MT | 68 mi | 1% | 7% |
| Lewis and Clark County, MT | 70 mi | 6% | 3% |
| Beaverhead County, MT | 91 mi | 6% | 9% |
Sources: USDA SSURGO (September 2, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status