Septic soil in Lyon County, KY, by the numbers
Very limited
64% of Lyon County, KY's surveyed soil comes back "Very limited" in USDA's own SSURGO data, the county's dominant condition for a septic absorption field. This is the reading that pushes a project toward an engineered system rather than a conventional one, and it covers 64% of Lyon County's land. Lyon County, KY is 213.785 square miles with a population of 9,078.
What Lyon County's reading doesn't cover
USDA's survey covers the whole of Lyon County, KY 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 Lyon County will actually do.
What a system would cost here
With 64% of Lyon 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, Lyon County, KY is the 2,637-most-constrained of 3,058 rated counties for septic soil. Within Kentucky alone it ranks 107 of 119.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems