New York County, NY: the USDA septic-suitability picture
Very limited
USDA puts New York County, NY at "Very limited" for septic absorption fields, the dominant reading across 89.3% of the county's soil. 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. For scale: 22.658 square miles and 1,660,664 people call New York County home.
Before you rely on this for one lot
New York County's rating is an average across the whole county, not a promise about any one lot inside it. The real answer for one lot is still a site-specific perc test, running about $750-$1,850 (typically near $1,300).
Budgeting for a system in New York County, NY
New York County's soil reading pushes the likely outcome toward an engineered system rather than a conventional one. Conventional systems run $3,000-$8,000 where they pass; where they don't, engineered alternatives (mound or aerobic treatment, whichever the health department requires) run $10,000-$40,000 - budget toward the higher figure until a perc test says otherwise.
New York County's rank among New York counties
Among the 3,058 rated counties on this site, New York County, NY ranks 1,338 most-constrained nationally, and 36 of 61 within New York.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems