St. Joseph County, MI: the USDA septic-suitability picture
Very limited
St. Joseph County, MI's SSURGO dominant class comes back "Very limited", covering 92.1% of the county. This is the reading that pushes a project toward an engineered system rather than a conventional one, and it covers 92.1% of St. Joseph County's land. The county spans 500.639 square miles, home to 61,171 people.
What this number does and doesn't tell you
Two lots a mile apart in St. Joseph County can carry different soil, even though they share one countywide rating. Budget $750-$1,850 for a real perc test on any specific parcel - that's the only figure a permit application accepts.
St. Joseph County: conventional vs. engineered cost
92.1% of St. Joseph 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.
How St. Joseph County, MI compares
Among the 3,058 rated counties on this site, St. Joseph County, MI ranks 1,026 most-constrained nationally, and 52 of 83 within Michigan.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems