Septic soil in Putnam County, IL, by the numbers

Very limited

Soil across 72% of Putnam County, IL rates "Very limited" in USDA's septic-absorption-field interpretation. This is the reading that pushes a project toward an engineered system rather than a conventional one, and it covers 72% of Putnam County's land. Putnam County, IL is 160.097 square miles with a population of 5,633.

What Putnam County's reading doesn't cover

Two lots a mile apart in Putnam County can carry different soil, even though they share one countywide rating. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Putnam County will actually do.

What a system would cost here

With 72% of Putnam 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.

Putnam County's rank among Illinois counties

Nationally, Putnam County, IL is the 2,402-most-constrained of 3,058 rated counties for septic soil. Within Illinois alone it ranks 79 of 101.

Before you act on this

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