White County, IL's soil, for a septic absorption field
Very limited
Soil across 90.3% of White County, IL rates "Very limited" in USDA's septic-absorption-field interpretation. Practically, that rules out a simple gravity system for most of the county - 90.3% of it sits in USDA's most-constrained bucket. White County, IL is 494.983 square miles with a population of 13,395.
What White County's reading doesn't cover
White 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 White County will actually do.
What a system would cost here
With 90.3% of White 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, White County, IL is the 1,236-most-constrained of 3,058 rated counties for septic soil. Within Illinois alone it ranks 48 of 101.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems