Jasper County, TX: the USDA septic-suitability picture
Very limited
Jasper County, TX's SSURGO dominant class comes back "Very limited", covering 86.8% of the county. Practically, that rules out a simple gravity system for most of the county - 86.8% of it sits in USDA's most-constrained bucket. The county spans 938.655 square miles, home to 32,907 people.
What this number does and doesn't tell you
Two lots a mile apart in Jasper 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.
Jasper County: conventional vs. engineered cost
86.8% of Jasper 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.
Jasper County's rank among Texas counties
Among the 3,058 rated counties on this site, Jasper County, TX ranks 1,559 most-constrained nationally, and 112 of 253 within Texas.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems