St. Clair County, Illinois
The most common soil here is Menfro, on about 10% of the land: a silt loam, smooth, like flour. Wakeland and Marine come next.
About 21% of the land drains well, and 60% stays wet for long stretches; groundwater comes within two feet of the surface under 61% of it.
USDA rates 85% of the land very limited for a standard septic drain field, and 71% very limited for homes with basements. That means extra cost or special design, not that it can't be done.
Worth knowing: 23% of the land floods occasionally or more.
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 St. Clair 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 Somewhat poorly drained and the dominant hydrologic group is C/D (varies with drainage). 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 St. Clair 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 |
|---|---|---|---|---|---|
| Wakeland silt loam, 0 to 2 percent slopes, frequently flooded | 32K | Somewhat poorly drained | B/D | Very limited | Very limited |
| Herrick silt loam, 0 to 2 percent slopes | 15K | Somewhat poorly drained | C/D | Very limited | Very limited |
| Cowden-Piasa silt loams, 0 to 2 percent slopes | 13K | Poorly drained | D | Very limited | Very limited |
| Bunkum-Coulterville silty clay loams, 5 to 10 percent slopes, severely eroded | 12K | Somewhat poorly drained | C/D | Very limited | Very limited |
| Marine silt loam, 0 to 2 percent slopes | 12K | Somewhat poorly drained | C/D | Very limited | Very limited |
| Homen silt loam, 2 to 5 percent slopes | 12K | Moderately well drained | C | Somewhat limited | Very limited |
| Winfield silt loam, 2 to 5 percent slopes | 11K | Moderately well drained | C | Somewhat limited | Very limited |
| Marine silt loam, 2 to 5 percent slopes | 10K | Somewhat poorly drained | C/D | Very limited | Very limited |
| Urban land | 10K | Not rated | Not rated | ||
| Water | 10K | Not rated | Not rated | ||
| Coulterville-Grantfork silty clay loams, 5 to 10 percent slopes, severely eroded | 9K | Somewhat poorly drained | C/D | Very limited | Very limited |
| Menfro silt loam, 2 to 5 percent slopes | 9K | Well drained | C | Somewhat limited | Somewhat limited |
| Menfro silt loam, 5 to 10 percent slopes, eroded | 8K | Well drained | B | Somewhat limited | Somewhat limited |
| Edwardsville silt loam, 0 to 2 percent slopes | 8K | Somewhat poorly drained | B/D | Very limited | Very limited |
| Coulterville-Darmstadt silt loams, 2 to 5 percent slopes, eroded | 8K | Somewhat poorly drained | D | Very limited | Very limited |
| Petrolia silty clay loam, 0 to 2 percent slopes, frequently flooded, long duration | 7K | Poorly drained | C/D | Very limited | Very limited |
| Bunkum-Atlas silty clay loams, 10 to 18 percent slopes, severely eroded | 7K | Somewhat poorly drained | C/D | Very limited | Very limited |
| Oconee-Darmstadt-Coulterville silt loams, 0 to 2 percent slopes | 7K | Somewhat poorly drained | C/D | Very limited | Very limited |
| Ruma-Ursa silty clay loams, 18 to 35 percent slopes, severely eroded | 6K | Well drained | B | Very limited | Very limited |
| Shaffton-Fluvents-Urban land complex, 0 to 2 percent slopes, occasionally flooded | 6K | Somewhat poorly drained | 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 71% of soils are rated "very limited" for dwellings with basements. Specific challenges include steep slopes, poor drainage in some areas, flood-prone areas. A geotechnical assessment is recommended before building.
Septic Systems
About 85% of soils are rated "very limited" for septic absorption fields. Poorly drained soils can't absorb septic effluent effectively. Engineered or alternative systems are frequently required. Always get a professional perc test before purchasing land that needs septic.
Gardening & Agriculture
Many soils hold water for extended periods. Raised beds are highly recommended to improve drainage for vegetables. Well-adapted native plants and water-loving species will do best in natural conditions.