Septic suitability in Johnson County, MO
Very limited
Johnson County, MO's SSURGO dominant class comes back "Very limited", covering 99.3% of the county. That reading means a conventional system is a poor bet here - 99.3% of Johnson County lands in the strictest "very limited" bucket USDA uses. The county spans 829.262 square miles, home to 55,880 people.
What this number does and doesn't tell you
Johnson County's rating is an average across the whole county, not a promise about any one lot inside it. Budget $750-$1,850 for a real perc test on any specific parcel - that's the only figure a permit application accepts.
Johnson County: conventional vs. engineered cost
99.3% of Johnson 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, Johnson County, MO ranks 44 most-constrained nationally, and 7 of 114 within Missouri.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems