Douglas County, MN's soil, for a septic absorption field
Very limited
73.9% of Douglas County, MN's surveyed soil comes back "Very limited" in USDA's own SSURGO data, the county's dominant condition for a septic absorption field. This is the reading that pushes a project toward an engineered system rather than a conventional one, and it covers 73.9% of Douglas County's land. Douglas County, MN is 636.882 square miles with a population of 39,933.
What Douglas County's reading doesn't cover
USDA's survey covers the whole of Douglas County, MN 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 Douglas County will actually do.
What a system would cost here
With 73.9% of Douglas 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, Douglas County, MN is the 2,333-most-constrained of 3,058 rated counties for septic soil. Within Minnesota alone it ranks 80 of 86.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems