Guide
How deep are wells in Montana?
There is no single answer, and any source that gives you one number for the whole state is not being straight with you. Montana well depth is driven by local geology and topographic position, and both change over remarkably short distances. What we can do is show you the recorded depths, county by county, and explain what drives the variation.
Recorded well depths by county — computed from state well logs
| County | Wells with depth | Median | Typical range | Median yield |
|---|---|---|---|---|
| Ravalli | 22,235 | 70 ft | 40–145 ft | 20 GPM |
| Flathead | 21,870 | 190 ft | 100–300 ft | 25 GPM |
| Gallatin | 19,863 | 80 ft | 54–154 ft | 30 GPM |
| Lewis And Clark | 17,222 | 103 ft | 59–191 ft | 20 GPM |
| Yellowstone | 15,126 | 35 ft | 25–76 ft | 24 GPM |
| Missoula | 15,324 | 100 ft | 62–170 ft | 30 GPM |
| Lincoln | 8,440 | 140 ft | 59.8–260 ft | 20 GPM |
| Lake | 8,067 | 180 ft | 95–324 ft | 25 GPM |
| Cascade | 7,235 | 105 ft | 36–240 ft | 22 GPM |
| Madison | 6,730 | 100 ft | 55–205 ft | 22 GPM |
| Park | 6,482 | 105 ft | 55–205 ft | 25 GPM |
| Carbon | 6,522 | 56 ft | 35.5–120 ft | 24 GPM |
| Stillwater | 5,764 | 59.4 ft | 32–125 ft | 20 GPM |
| Rosebud | 4,291 | 100 ft | 41–200 ft | 10 GPM |
| Toole | 853 | 38 ft | 20–115 ft | 10 GPM |
| Jefferson | 5,400 | 180 ft | 90–300 ft | 20 GPM |
| Powder River | 4,023 | 170 ft | 80–300 ft | 10 GPM |
| Richland | 4,923 | 80 ft | 40–164.5 ft | 11 GPM |
| Beaverhead | 5,022 | 76 ft | 42–143 ft | 20 GPM |
| Big Horn | 4,306 | 104 ft | 38–300 ft | 12 GPM |
| Silver Bow | 4,396 | 90 ft | 40–162.3 ft | 20 GPM |
| Sanders | 4,834 | 162.7 ft | 70–300 ft | 25 GPM |
| Musselshell | 3,610 | 170 ft | 80–300 ft | 9 GPM |
| Roosevelt | 3,802 | 60 ft | 30–116 ft | 10 GPM |
| Hill | 3,229 | 90 ft | 33–159 ft | 12 GPM |
| Fergus | 3,844 | 120 ft | 43.8–280 ft | 15 GPM |
| Glacier | 1,391 | 90 ft | 38–160 ft | 12 GPM |
| Dawson | 3,780 | 87 ft | 37–161 ft | 10 GPM |
| Broadwater | 4,020 | 140 ft | 80–240 ft | 25 GPM |
| Teton | 2,969 | 30 ft | 20–64 ft | 15 GPM |
| Phillips | 2,530 | 70 ft | 35–190 ft | 11 GPM |
| Custer | 3,219 | 180 ft | 74–320 ft | 15 GPM |
| Valley | 3,063 | 66 ft | 38–118 ft | 10 GPM |
| Sheridan | 2,416 | 100 ft | 43–170 ft | 10 GPM |
| Blaine | 1,732 | 77.3 ft | 42–180 ft | 15 GPM |
| Chouteau | 2,343 | 38 ft | 23–107.3 ft | 10 GPM |
| Fallon | 1,869 | 170 ft | 76–380 ft | 10 GPM |
| Deer Lodge | 2,550 | 60 ft | 39–140 ft | 20 GPM |
| Pondera | 1,220 | 38 ft | 18–90 ft | 10 GPM |
| Granite | 2,440 | 80 ft | 45–180 ft | 20 GPM |
| Powell | 2,471 | 82 ft | 50–157 ft | 20 GPM |
| Garfield | 2,288 | 174.5 ft | 100–280 ft | 10 GPM |
| Sweet Grass | 2,352 | 82.5 ft | 45–160 ft | 20 GPM |
| Mccone | 1,959 | 112 ft | 60–190 ft | 10 GPM |
| Liberty | 1,027 | 38 ft | 20–140.1 ft | 10 GPM |
| Carter | 1,589 | 155 ft | 70–260 ft | 10 GPM |
| Prairie | 1,820 | 130 ft | 47–270.5 ft | 10 GPM |
| Mineral | 1,896 | 117 ft | 60–180 ft | 30 GPM |
| Judith Basin | 1,587 | 100 ft | 40–231.5 ft | 15 GPM |
| Wibaux | 1,381 | 125 ft | 57.8–230 ft | 8 GPM |
| Daniels | 1,456 | 55 ft | 30–104.3 ft | 7 GPM |
| Meagher | 1,390 | 100 ft | 52–183 ft | 20 GPM |
| Wheatland | 1,053 | 100 ft | 53.5–180 ft | 16 GPM |
| Petroleum | 637 | 150 ft | 31–860 ft | 10 GPM |
| Golden Valley | 1,016 | 90 ft | 38–170 ft | 10 GPM |
| Treasure | 863 | 80 ft | 38–170 ft | 10 GPM |
Source: Montana Bureau of Mines and Geology, Ground Water Information Center (GWIC). Abandoned, plugged, and destroyed wells and implausible depths are excluded. Counties with fewer than 50 depth records are not shown, because a median from a handful of wells would mislead.
Why the range is so wide
Most of Montana's population lives in intermontane basins — the broad valleys around Bozeman, Missoula, Kalispell, Helena, and the Bitterroot. These basins are filled with unconsolidated sediment: sand, gravel, silt, and clay washed down over millions of years. Where that basin fill is saturated and thick, wells can be shallow and productive, sometimes under 100 feet.
Move toward the edge of the basin and the picture changes quickly. The unconsolidated fill thins and gives way to bedrock — Cretaceous shale, volcanic rock, or crystalline basement. Wells in those units are typically deeper, often lower-yielding, and much harder to predict, because water moves through fractures rather than through pore space between grains. Two properties a mile apart can sit on opposite sides of that transition.
This is why a county median is orientation rather than prediction. It tells you what is normal across a large and geologically mixed area. It does not tell you what a driller will find on one parcel.
What a depth estimate can honestly tell you
The defensible approach is comparison. Look at wells close to the property, prefer the ones in the same geologic unit, weight them by how similar and how well-located they are, and report a range rather than a point.
That is what our property reports do. We select comparable wells around the specific parcel, expanding the search radius only as far as needed to gather enough records, and we report both a likely range and a wider band showing where 80% of comparable wells fall. We also state a confidence rating, because a range built on eight wells deserves less trust than one built on forty.
What drilling depth means for cost
Drilling is typically priced per foot, with additional cost for casing, and the pump has to be set below the water level. So depth affects the project twice: the borehole itself, and the equipment needed to lift water from it.
This is why the range matters more than the median. If comparable wells near a property run from 120 to 400 feet, the difference between the good and bad outcome is a materially different budget. A report that hands you one number hides exactly the risk you needed to see.
This guide is general information for property research, not legal, engineering, or hydrogeologic advice. Verify anything that matters to a transaction with Montana DNRC, the Montana Bureau of Mines and Geology, and qualified professionals.