Septic suitability in Silver Bow County, MT
Very limited
Silver Bow County, MT: USDA's soil survey calls 67.7% of the county "Very limited" for a septic leach field. Expect the ground itself to work against a plain gravity system; USDA's strictest bucket alone covers 67.7% of the county. The county spans 717.99 square miles, home to 36,134 people.
What this number does and doesn't tell you
Silver Bow County's rating is an average across the whole county, not a promise about any one lot inside it. Budget $750-$1,850 for a real perc test on any specific parcel - that's the only figure a permit application accepts.
Silver Bow County: conventional vs. engineered cost
67.7% of Silver Bow County carrying a "Very limited" reading changes the realistic budget here. Conventional systems run $3,000-$8,000 where they pass; where they don't, engineered alternatives (mound or aerobic treatment, whichever the health department requires) run $10,000-$40,000 - budget toward the higher figure until a perc test says otherwise.
Where this sits nationally
Among the 3,058 rated counties on this site, Silver Bow County, MT ranks 2,538 most-constrained nationally, and 49 of 54 within Montana.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems