Septic soil in Milam County, TX, by the numbers
Very limited
Soil across 83.2% of Milam County, TX rates "Very limited" in USDA's septic-absorption-field interpretation. Practically, that rules out a simple gravity system for most of the county - 83.2% of it sits in USDA's most-constrained bucket. Milam County, TX is 1,016.356 square miles with a population of 26,159.
What Milam County's reading doesn't cover
Nothing about Milam County, TX's SSURGO figure applies to a specific address - it's a county-wide average. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Milam County will actually do.
What a system would cost here
With 83.2% of Milam 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.
How Milam County, TX compares
Nationally, Milam County, TX is the 1,842-most-constrained of 3,058 rated counties for septic soil. Within Texas alone it ranks 134 of 253.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems