Johnson County, Illinois
The most common soil here is Hosmer, on about 27% of the land: a silt loam, smooth, like flour. Grantsburg and Zanesville come next.
About 21% of the land drains well, and 16% stays wet for long stretches; groundwater comes within two feet of the surface under 16% of it.
USDA rates 93% of the land very limited for a standard septic drain field, and 35% very limited for homes with basements. That means extra cost or special design, not that it can't be done.
Worth knowing: 21% of the land floods occasionally or more, and bedrock lies within 40 inches under 17% of it.
Soils change over short distances, so look up an address below for the soil at that exact spot and the reasons behind each rating.
The soils you're most likely standing on
The biggest named soils in Johnson County, Illinois, each drawn five feet deep from its official USDA description, in its recorded colors.
Dots mark gravel; white flecks mark lime. Shares are by acres across the survey area, and each mapped patch usually mixes several of these soils.
The biggest mapped areas
The dominant drainage class is Moderately well drained and the dominant hydrologic group is C (slow infiltration, moderate runoff). The most common soil order is Alfisols — moderately leached forest soils with a clay-enriched subsoil. 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. Search your address to find the exact soil composition, drainage, and series details at your specific location.
| 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 |
Soil Orders in This Area
The USDA classifies every soil into one of 12 soil orders. Here are the dominant orders found in this survey area.
What This Means
Building & Foundations
About 35% of soils have significant building limitations, while the rest are generally suitable. Check specific sites carefully — conditions vary across the area.
Septic Systems
About 93% 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.