Septic suitability in McClain County, OK
Very limited
McClain County, OK's SSURGO dominant class comes back "Very limited", covering 69.5% of the county. Expect the ground itself to work against a plain gravity system; USDA's strictest bucket alone covers 69.5% of the county. The county spans 570.72 square miles, home to 48,434 people.
What this number does and doesn't tell you
USDA's survey covers the whole of McClain County, OK at once, not any single address. Budget $750-$1,850 for a real perc test on any specific parcel - that's the only figure a permit application accepts.
McClain County: conventional vs. engineered cost
69.5% of McClain County carrying a "Very limited" reading changes the realistic budget here. 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.
Where this sits nationally
Among the 3,058 rated counties on this site, McClain County, OK ranks 2,479 most-constrained nationally, and 65 of 77 within Oklahoma.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems