Septic suitability in Jersey County, IL
Very limited
Jersey County, IL's SSURGO dominant class comes back "Very limited", covering 73.2% of the county. A standard gravity system routinely fails on ground like this; the same share of the county falls in USDA's worst absorption-field bucket outright. The county spans 369.556 square miles, home to 21,150 people.
What this number does and doesn't tell you
Two lots a mile apart in Jersey County can carry different soil, even though they share one countywide rating. Budget $750-$1,850 for a real perc test on any specific parcel - that's the only figure a permit application accepts.
Jersey County: conventional vs. engineered cost
73.2% of Jersey County carrying a "Very limited" reading changes the realistic budget here. Conventional systems run $3,000-$8,000 where they pass; where they don't, engineered alternatives (mound or aerobic treatment, whichever the health department requires) run $10,000-$40,000 - budget toward the higher figure until a perc test says otherwise.
Where this sits nationally
Among the 3,058 rated counties on this site, Jersey County, IL ranks 2,365 most-constrained nationally, and 76 of 101 within Illinois.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems