Septic soil in Montgomery County, IL, by the numbers

Very limited

Soil across 93.4% of Montgomery County, IL rates "Very limited" in USDA's septic-absorption-field interpretation. Expect the ground itself to work against a plain gravity system; USDA's strictest bucket alone covers 93.4% of the county. Montgomery County, IL is 703.766 square miles with a population of 27,615.

What Montgomery County's reading doesn't cover

Nothing about Montgomery 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 Montgomery County will actually do.

What a system would cost here

With 93.4% of Montgomery 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.

Montgomery County's rank among Illinois counties

Nationally, Montgomery County, IL is the 873-most-constrained of 3,058 rated counties for septic soil. Within Illinois alone it ranks 38 of 101.

Before you act on this

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