Septic soil in Toole County, MT, by the numbers
Very limited
Soil across 85.6% of Toole County, MT rates "Very limited" in USDA's septic-absorption-field interpretation. That reading means a conventional system is a poor bet here - 85.6% of Toole County lands in the strictest "very limited" bucket USDA uses. Toole County, MT is 1,914.864 square miles with a population of 5,153.
What Toole County's reading doesn't cover
USDA's survey covers the whole of Toole County, MT at once, not any single address. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Toole County will actually do.
What a system would cost here
With 85.6% of Toole County rating "Very limited", a standard gravity system is not a safe assumption here. The engineered-system range, $10,000-$40,000 (mound or aerobic treatment), is the more realistic number to plan around, against $3,000-$8,000 for a conventional system on the rare lot that passes.
Where this sits nationally
Nationally, Toole County, MT is the 1,650-most-constrained of 3,058 rated counties for septic soil. Within Montana alone it ranks 12 of 54.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems