Johnson County, Illinois
The dominant drainage class is Moderately well drained and the dominant hydrologic group is C (slow infiltration, moderate runoff). This report summarizes the major soil map units across the survey area to help you understand what to expect when buying, building, or gardening in Johnson County, Illinois.
| Soil Map Unit | Acres | Drainage | Hydro Group | Dwellings | Septic |
|---|---|---|---|---|---|
| Wellston-Berks complex, 18 to 35 percent slopes | 21K | Well drained | B | Very limited | Very limited |
| Hosmer silt loam, 10 to 18 percent slopes, severely eroded | 19K | Moderately well drained | C | Somewhat limited | Very limited |
| Hosmer silt loam, 5 to 10 percent slopes, eroded | 16K | Moderately well drained | C | Somewhat limited | Very limited |
| Zanesville silt loam, 10 to 18 percent slopes, severely eroded | 15K | Moderately well drained | C | Somewhat limited | Very limited |
| Hosmer silt loam, 2 to 5 percent slopes | 13K | Moderately well drained | C | Somewhat limited | Very limited |
| Belknap silt loam, 0 to 2 percent slopes, occasionally flooded | 13K | Somewhat poorly drained | B/D | Very limited | Very limited |
| Grantsburg silt loam, 5 to 10 percent slopes, severely eroded | 12K | Moderately well drained | C | Somewhat limited | Very limited |
| Grantsburg silt loam, 2 to 5 percent slopes | 11K | Moderately well drained | C | Somewhat limited | Very limited |
| Hosmer silt loam, 5 to 10 percent slopes, severely eroded | 11K | Moderately well drained | C | Somewhat limited | Very limited |
| Wellston-Berks complex, 10 to 18 percent slopes, eroded | 10K | Well drained | B | Somewhat limited | Somewhat limited |
| Sharon silt loam, 0 to 3 percent slopes, occasionally flooded | 9K | Moderately well drained | B | Very limited | Very limited |
| Grantsburg silt loam, 5 to 10 percent slopes, eroded | 8K | Moderately well drained | C | Somewhat limited | Very limited |
| Hosmer silt loam, 10 to 18 percent slopes, eroded | 7K | Moderately well drained | C | Somewhat limited | Very limited |
| Zanesville silt loam, 10 to 18 percent slopes, eroded | 5K | Moderately well drained | D | Somewhat limited | Very limited |
| Bonnie and Petrolia soils, undrained, 0 to 2 percent slopes, frequently flooded | 5K | Poorly drained | C/D | Very limited | Very limited |
| Grantsburg silt loam, 10 to 18 percent slopes, severely eroded | 5K | Moderately well drained | C | Somewhat limited | Very limited |
| Bonnie silt loam, 0 to 2 percent slopes, occasionally flooded | 4K | Poorly drained | C/D | Very limited | Very limited |
| Berks, Muskingum, and Weikert soils, 35 to 70 percent slopes | 4K | Well drained | B | Very limited | Very limited |
| Zanesville silt loam, 5 to 10 percent slopes, severely eroded | 4K | Moderately well drained | D | Somewhat limited | Very limited |
| Burnside silt loam, 1 to 4 percent slopes, occasionally flooded | 4K | Well drained | B | Very limited | Very limited |
What This Means
Building & Foundations
About 30% of soils have significant building limitations, while the rest are generally suitable. Check specific sites carefully — conditions vary across the area.
Septic Systems
About 94% of soils are rated "very limited" for septic absorption fields. Despite good drainage overall, limitations may stem from shallow bedrock, steep slopes, or seasonal conditions. Engineered or alternative systems are frequently required. Always get a professional perc test before purchasing land that needs septic.
Gardening & Agriculture
Well-drained soils on sloped terrain — good for most plants but watch for erosion. Terracing, contour planting, and mulching help retain moisture and topsoil. Drip irrigation is more effective than sprinklers on slopes.