Septic suitability in Fulton County, IL
Very limited
Fulton County, IL: USDA's soil survey calls 58.9% of the county "Very limited" for a septic leach field. That reading means a conventional system is a poor bet here - 58.9% of Fulton County lands in the strictest "very limited" bucket USDA uses. The county spans 865.694 square miles, home to 32,510 people.
What this number does and doesn't tell you
USDA's survey covers the whole of Fulton 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.
Fulton County: conventional vs. engineered cost
58.9% of Fulton 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, Fulton County, IL ranks 2,741 most-constrained nationally, and 94 of 101 within Illinois.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems