Sangamon County's SSURGO septic rating
Very limited
USDA puts Sangamon County, IL at "Very limited" for septic absorption fields, the dominant reading across 72.9% of the county's soil. That reading means a conventional system is a poor bet here - 72.9% of Sangamon County lands in the strictest "very limited" bucket USDA uses. The county spans 868.23 square miles, home to 194,345 people.
What this number does and doesn't tell you
USDA's survey covers the whole of Sangamon County, IL at once, not any single address. Budget $750-$1,850 for a real perc test on any specific parcel - that's the only figure a permit application accepts.
Sangamon County: conventional vs. engineered cost
72.9% of Sangamon 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.
Sangamon County's rank among Illinois counties
Among the 3,058 rated counties on this site, Sangamon County, IL ranks 2,373 most-constrained nationally, and 77 of 101 within Illinois.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems