Septic soil in Stephenson County, IL, by the numbers

Very limited

In Stephenson County, IL, 58% of the surveyed land carries a "Very limited" rating for a standard septic drain field. Practically, that rules out a simple gravity system for most of the county - 58% of it sits in USDA's most-constrained bucket. Stephenson County, IL is 564.247 square miles with a population of 43,088.

What Stephenson County's reading doesn't cover

Nothing about Stephenson County, IL's SSURGO figure applies to a specific address - it's a county-wide average. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Stephenson County will actually do.

What a system would cost here

With 58% of Stephenson 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, Stephenson County, IL is the 2,763-most-constrained of 3,058 rated counties for septic soil. Within Illinois alone it ranks 95 of 101.

Before you act on this

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