Septic soil in Issaquena County, MS, by the numbers
Very limited
89.9% of Issaquena County, MS's surveyed soil comes back "Very limited" in USDA's own SSURGO data, the county's dominant condition for a septic absorption field. That reading means a conventional system is a poor bet here - 89.9% of Issaquena County lands in the strictest "very limited" bucket USDA uses. Issaquena County, MS is 412.98 square miles with a population of 1,295.
What Issaquena County's reading doesn't cover
Two lots a mile apart in Issaquena County can carry different soil, even though they share one countywide rating. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Issaquena County will actually do.
What a system would cost here
With 89.9% of Issaquena 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.
Issaquena County's rank among Mississippi counties
Nationally, Issaquena County, MS is the 1,283-most-constrained of 3,058 rated counties for septic soil. Within Mississippi alone it ranks 52 of 82.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems