Johnson County, GA: the USDA septic-suitability picture
Very limited
USDA puts Johnson County, GA at "Very limited" for septic absorption fields, the dominant reading across 76.9% of the county's soil. That reading means a conventional system is a poor bet here - 76.9% of Johnson County lands in the strictest "very limited" bucket USDA uses. The county spans 303.019 square miles, home to 9,178 people.
What this number does and doesn't tell you
USDA's survey covers the whole of Johnson County, GA 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.
Johnson County: conventional vs. engineered cost
76.9% 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, GA ranks 2,183 most-constrained nationally, and 65 of 159 within Georgia.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems