Jones County, SD's soil, for a septic absorption field
Very limited
95.5% of Jones County, SD's surveyed soil comes back "Very limited" in USDA's own SSURGO data, the county's dominant condition for a septic absorption field. That reading means a conventional system is a poor bet here - 95.5% of Jones County lands in the strictest "very limited" bucket USDA uses. Jones County, SD is 969.668 square miles with a population of 874.
What Jones County's reading doesn't cover
Jones County's rating is an average across the whole county, not a promise about any one lot inside it. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Jones County will actually do.
What a system would cost here
With 95.5% of Jones 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, Jones County, SD is the 603-most-constrained of 3,058 rated counties for septic soil. Within South Dakota alone it ranks 6 of 66.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems