Soil series profile
St. Charles soil series
St. Charles is a well drained soil with a silt loam surface, mapped on 271,206 acres in 45 counties across 3 states. Hydrologic group B.
- Drainage class
- Well drained 81% of mapped acres
- Hydrologic group
- B 95% of mapped acres
- Typical topsoil pH
- 6.5 slightly acidic · range 6.5–6.7
- Mapped area
- 271k acres in 45 counties, 3 states
Typical St. Charles profile
Texture and pH by depth
Show as a table
| Depth | Texture | pH | Clay | Sand | Organic matter |
|---|---|---|---|---|---|
| 0–8 in (Ap) | Silt loam | 6.5 | 23% | 10% | 3% |
| 8–45 in (Bt1) | Silty clay loam | 5.9 | 35% | 10% | 1% |
| 45–50 in (2Bt2) | Loam | 6.2 | 15% | 50% | 0.25% |
| 50–79 in (2C) | Sandy loam | 8.2 | 10% | 75% | 0.25% |
What this means
What St. Charles soil means for gardens, lawns and septic systems
For gardens
Typical topsoil in St. Charles soils is slightly acidic: pH 6.5 (most land between 6.5 and 6.7), the range most vegetables, flowers and lawn grasses prefer.
Loamy topsoil (loam, silt loam and similar) covers 96% of mapped St. Charles acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silt loam (96% of mapped St. Charles acres).
100% of mapped St. Charles acres is moderately well to excessively drained, which suits most garden plants.
For lawns and yards
Most land is in hydrologic groups B and C, where rain soaks in at a moderate pace.
For a septic system
For conventional septic absorption fields, NRCS rates 79% of the acres in mapped St. Charles soils very limited, 18% somewhat limited and 0% not limited (4% not rated, such as urban land, pits or water).
Where the soil is very limited (slow permeability, a high water table, flooding, shallow bedrock or steep slopes), alternative systems such as mound or sand-filter designs are common and cost more.
Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.
Where St. Charles soil is found
Mapped acres
St. Charles is mapped in Wisconsin, Illinois and Indiana.
| County | Acres | Share of county land |
|---|---|---|
| Dodge County, WI | 65,259 | 11.7% |
| Dane County, WI | 43,157 | 5.6% |
| Columbia County, WI | 24,577 | 5.0% |
| Rock County, WI | 23,527 | 5.1% |
| Walworth County, WI | 20,595 | 5.8% |
| Fond du Lac County, WI | 11,860 | 2.6% |
| Sauk County, WI | 7,827 | 1.5% |
| Waukesha County, WI | 7,029 | 2.0% |
| Boone County, IL | 6,859 | 3.9% |
| LaSalle County, IL | 6,276 | 0.9% |
| Washington County, WI | 5,783 | 2.1% |
| Green Lake County, WI | 5,363 | 2.4% |
| Ogle County, IL | 5,263 | 1.1% |
| Winnebago County, IL | 4,870 | 1.6% |
| Sheboygan County, WI | 3,361 | 1.0% |
| Tazewell County, IL | 3,078 | 0.8% |
| Stephenson County, IL | 3,040 | 0.9% |
| Montgomery County, IN | 2,902 | 0.9% |
| Jefferson County, WI | 2,455 | 0.7% |
| Logan County, IL | 2,390 | 0.6% |
| Bureau County, IL | 2,267 | 0.4% |
| Stark County, IL | 1,697 | 0.9% |
| De Witt County, IL | 1,437 | 0.6% |
| Fulton County, IL | 1,404 | 0.3% |
| Winnebago County, WI | 1,313 | 0.5% |
| Peoria County, IL | 1,126 | 0.3% |
| Marshall County, IL | 949 | 0.4% |
| Menard County, IL | 802 | 0.4% |
| Schuyler County, IL | 784 | 0.3% |
| Kenosha County, WI | 758 | 0.4% |
| Lee County, IL | 609 | 0.1% |
| Woodford County, IL | 583 | 0.2% |
| Piatt County, IL | 482 | 0.2% |
| Racine County, WI | 457 | 0.2% |
| Edgar County, IL | 370 | 0.1% |
| Calumet County, WI | 287 | 0.1% |
| Kendall County, IL | 158 | 0.1% |
| McHenry County, IL | 56 | 0.0% |
| Milwaukee County, WI | 50 | 0.0% |
| Kane County, IL | 38 | 0.0% |
| Fountain County, IN | 37 | 0.0% |
| Green County, WI | 26 | 0.0% |
| Manitowoc County, WI | 20 | 0.0% |
| McLean County, IL | 16 | 0.0% |
| Ozaukee County, WI | 10 | 0.0% |
Septic absorption fields
NRCS rating, share of St. Charles acres
Show as a table
| Category | Share of acres |
|---|---|
| Not limited | 0.0% |
| Somewhat limited | 17.6% |
| Very limited | 78.8% |
| Not rated | 3.6% |
Drainage, water table and flooding
Share of St. Charles acres
- Depth to seasonal high water table
- About 3.9 feet (47 in) (median where reported).
- Flooding
- Not mapped as flooding on most acres.
- Slope
- Typically 1–8% (median 4%).
- Topsoil organic matter
- Median 2%.
Drainage class
Show as a table
| Category | Share of acres |
|---|---|
| Excessively drained | 0.0% |
| Somewhat excessively drained | 0.0% |
| Well drained | 81.4% |
| Moderately well drained | 18.6% |
| Somewhat poorly drained | 0.0% |
| Poorly drained | 0.0% |
| Very poorly drained | 0.0% |
Hydrologic soil group
Show as a table
| Category | Share of acres |
|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 0.0% |
| B: moderate infiltration | 94.6% |
| C: slow infiltration | 0.1% |
| D: very slow infiltration (clayey, shallow or wet) | 0.0% |
| A/D: D as is, A if drained | 0.0% |
| B/D: D as is, B if drained | 0.0% |
| C/D: D as is, C if drained | 0.0% |
| Not rated | 5.3% |
Sources & data dates
- Source
- USDA NRCS Soil Survey Geographic Database (SSURGO), queried through Soil Data Access. Public domain.
- Data date
- SSURGO as published on November 3, 2026 (most recent survey area update October 26, 2026). NRCS refreshes SSURGO each October.
- Scope
- All map unit components named St. Charles (component kind "Series") in SSURGO: 271,206 acres.
- Method
- Shares are by mapped acres of St. Charles components. The profile comes from the single largest St. Charles component. Full methodology.