Septic soil in Orange County, TX, by the numbers
Very limited
In Orange County, TX, 80.5% of the surveyed land carries a "Very limited" rating for a standard septic drain field. Expect the ground itself to work against a plain gravity system; USDA's strictest bucket alone covers 80.5% of the county. Orange County, TX is 333.799 square miles with a population of 86,115.
What Orange County's reading doesn't cover
Orange County's rating is an average across the whole county, not a promise about any one lot inside it. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Orange County will actually do.
What a system would cost here
With 80.5% of Orange 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, Orange County, TX is the 2,017-most-constrained of 3,058 rated counties for septic soil. Within Texas alone it ranks 152 of 253.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems