Jefferson County's SSURGO septic rating
Very limited
Jefferson County, ID: USDA's soil survey calls 81.1% of the county "Very limited" for a septic leach field. Expect the ground itself to work against a plain gravity system; USDA's strictest bucket alone covers 81.1% of the county. The county spans 1,093.681 square miles, home to 34,854 people.
What this number does and doesn't tell you
Nothing about Jefferson County, ID's SSURGO figure applies to a specific address - it's a county-wide average. Budget $750-$1,850 for a real perc test on any specific parcel - that's the only figure a permit application accepts.
Jefferson County: conventional vs. engineered cost
81.1% of Jefferson 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, Jefferson County, ID ranks 1,986 most-constrained nationally, and 32 of 44 within Idaho.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems