Gallatin County, Montana
USDA's soil survey flags shrink-swell clay on 9% of Gallatin County's mapped land and a shallow water table under basements on 9%, both below the national shares of 15% and 29%. None of the county is in drought on the October 13, 2026 Drought Monitor map, after 1.2% a week earlier.
FEMA's flood data list 13 flood losses here since 2016. 29% of homes were built before 1980, against 50% nationally; the median home dates from 1998.
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 Gallatin County
| Expansive clay (limits slab homes) | 9.0% |
| High water table (limits basements) | 8.7% |
| Septic fields very limited | 67.7% |
| Clay swell (LEP, by area) | 3.1% |
| High-swell land (LEP 6%+) | 9.7% |
| Mapped soil | 1,601,993 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Brocko | 3% | n/a |
| Amesha | 2% | n/a |
| Amsterdam | 2% | n/a |
| Quagle | 1% | n/a |
| Bangtail | 1% | n/a |
| Blackdog | 1% | n/a |
How we count · survey areas MT622 (2025-08-30), MT623 (2025-08-30)
What the numbers mean here
Rain over the 12 months to August 2026: 24.01 in, 0.43 in below the 1991-2020 average year of 24.44 in.
USDA rates 68% of the land very limited for septic absorption fields.
With shrink-swell clay on 9% and a shallow water table on 9% of the land, the soil survey points to neither problem across most of Gallatin 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 51 of the last 52 weeks; the most was 100% of its area, in 22 weeks, most recently on the August 25, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 27.4% |
| D1 moderate drought or worse | 0% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
13 flood losses since 2016, $58,342 paid. The worst year was 2018, with 4.
| Year | Flood losses |
|---|---|
| 2016 | 0 |
| 2017 | 0 |
| 2018 | 4 |
| 2019 | 2 |
| 2020 | 1 |
| 2021 | 0 |
| 2022 | 3 |
| 2023 | 2 |
| 2024 | 1 |
| 2025 | 0 |
| 2026 to date | 0 |
Rain
| Average year, 1991-2020 | 24.44 in |
| 12 months to August 2026 | 24.01 in (-0.43) |
| 2025 | 23.93 in (-0.51) |
| Wettest year since 1895 | 1975: 32.97 in |
| Driest year since 1895 | 1934: 16.18 in |
| Days with 1 inch or more, normal at BOZEMAN 6 W EXP FARM (11 mi away) | 0.8 |
Homes
| Housing units | 57,568 |
| Median year built | 1998 |
| Built before 1980 | 29% |
| Built 2000 or later | 47% |
| Owner-occupied | 61% |
| Median value, owner-occupied | $667,600 |
| Single-family detached | 58% |
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 |
|---|---|---|---|
| Park County, MT | 31 mi | 11% | 4% |
| Madison County, MT | 39 mi | 3% | 4% |
| Broadwater County, MT | 59 mi | 1% | 3% |
| Jefferson County, MT | 60 mi | 1% | 7% |
| Sweet Grass County, MT | 62 mi | 16% | 5% |
| Meagher County, MT | 76 mi | n/a | n/a |
| Silver Bow County, MT | 77 mi | 2% | 5% |
| Stillwater County, MT | 87 mi | 26% | 5% |
Sources: USDA SSURGO (August 30, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status