Guadalupe County, TX's soil, for a septic absorption field
Very limited
89.1% of Guadalupe County, TX's surveyed soil comes back "Very limited" in USDA's own SSURGO data, the county's dominant condition for a septic absorption field. Practically, that rules out a simple gravity system for most of the county - 89.1% of it sits in USDA's most-constrained bucket. Guadalupe County, TX is 711.252 square miles with a population of 195,166.
What Guadalupe County's reading doesn't cover
USDA's survey covers the whole of Guadalupe County, TX at once, not any single address. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Guadalupe County will actually do.
What a system would cost here
With 89.1% of Guadalupe 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.
Where this sits nationally
Nationally, Guadalupe County, TX is the 1,363-most-constrained of 3,058 rated counties for septic soil. Within Texas alone it ranks 100 of 253.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems