Septic soil in Monroe County, FL, by the numbers
Very limited
In Monroe County, FL, 74.8% of the surveyed land carries a "Very limited" rating for a standard septic drain field. Practically, that rules out a simple gravity system for most of the county - 74.8% of it sits in USDA's most-constrained bucket. Monroe County, FL is 983.043 square miles with a population of 80,908.
What Monroe County's reading doesn't cover
USDA's survey covers the whole of Monroe County, FL 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 Monroe County will actually do.
What a system would cost here
With 74.8% of Monroe 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, Monroe County, FL is the 2,292-most-constrained of 3,058 rated counties for septic soil. Within Florida alone it ranks 54 of 65.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems