Harris County's SSURGO septic rating
Very limited
USDA puts Harris County, TX at "Very limited" for septic absorption fields, the dominant reading across 87.2% of the county's soil. Practically, that rules out a simple gravity system for most of the county - 87.2% of it sits in USDA's most-constrained bucket. For scale: 1,707.103 square miles and 5,009,302 people call Harris County home.
Before you rely on this for one lot
USDA's survey covers the whole of Harris County, TX at once, not any single address. The real answer for one lot is still a site-specific perc test, running about $750-$1,850 (typically near $1,300).
Budgeting for a system in Harris County, TX
Harris County's soil reading pushes the likely outcome toward an engineered system rather than a conventional one. 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, Harris County, TX ranks 1,527 most-constrained nationally, and 110 of 253 within Texas.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems