DeKalb County, IL's soil, for a septic absorption field

Very limited

Soil across 99.6% of DeKalb County, IL rates "Very limited" in USDA's septic-absorption-field interpretation. That reading means a conventional system is a poor bet here - 99.6% of DeKalb County lands in the strictest "very limited" bucket USDA uses. DeKalb County covers 631.337 square miles and counts 101,335 residents.

This is a county figure, not a parcel figure

Nothing about DeKalb County, IL's SSURGO figure applies to a specific address - it's a county-wide average. A site-specific perc test, usually $750-$1,850, is what a health department will actually require before permitting a lot in DeKalb County.

System cost, conventional vs. engineered

Given DeKalb County's rating, plan for the engineered-system range rather than the conventional one. 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, DeKalb County, IL is the 16-most-constrained of 3,058 rated counties for septic soil. Within Illinois alone it ranks 3 of 101.

Further reading

How this rating is built, and its real limits · Conventional vs. engineered septic systems