Rock County, MN's soil, for a septic absorption field
Very limited
92.7% of Rock 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. Expect the ground itself to work against a plain gravity system; USDA's strictest bucket alone covers 92.7% of the county. Rock County, MN is 482.459 square miles with a population of 9,525.
What Rock County's reading doesn't cover
Two lots a mile apart in Rock County can carry different soil, even though they share one countywide rating. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Rock County will actually do.
What a system would cost here
With 92.7% of Rock 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.
Rock County's rank among Minnesota counties
Nationally, Rock County, MN is the 967-most-constrained of 3,058 rated counties for septic soil. Within Minnesota alone it ranks 33 of 86.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems