Septic soil in Forsyth County, NC, by the numbers
Very limited
Soil across 53.6% of Forsyth County, NC rates "Very limited" in USDA's septic-absorption-field interpretation. A standard gravity system routinely fails on ground like this; the same share of the county falls in USDA's worst absorption-field bucket outright. Forsyth County, NC is 408.046 square miles with a population of 398,143.
What Forsyth County's reading doesn't cover
Nothing about Forsyth County, NC'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 Forsyth County will actually do.
What a system would cost here
With 53.6% of Forsyth 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.
Forsyth County's rank among North Carolina counties
Nationally, Forsyth County, NC is the 2,839-most-constrained of 3,058 rated counties for septic soil. Within North Carolina alone it ranks 83 of 97.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems