What Miami County, OH's soil rates for a septic system
Very limited
98.6% of Miami County, OH's surveyed soil comes back "Very limited" in USDA's own SSURGO data, the county's dominant condition for a septic absorption field. 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. Miami County, OH is 406.581 square miles with a population of 111,950.
What Miami County's reading doesn't cover
Nothing about Miami County, OH'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 Miami County will actually do.
What a system would cost here
With 98.6% of Miami 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.
Miami County's rank among Ohio counties
Nationally, Miami County, OH is the 144-most-constrained of 3,058 rated counties for septic soil. Within Ohio alone it ranks 15 of 87.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems