Mason County, Illinois
The most common soil here is Plainfield, on about 11% of the land: a sand, loose sand that holds almost no water. Onarga and Bloomfield come next.
About 54% of the land drains well, and 40% stays wet for long stretches; groundwater comes within two feet of the surface under 41% of it.
USDA rates 90% of the land very limited for a standard septic drain field, and 43% very limited for homes with basements. That means extra cost or special design, not that it can't be done.
Worth knowing: 12% 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 Mason 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 Excessively drained and the dominant hydrologic group is A (high infiltration, low runoff). The most common soil order is Mollisols — grassland soils with a thick, dark, fertile topsoil rich in organic matter. 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 Mason 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 |
|---|---|---|---|---|---|
| Plainfield sand, 1 to 7 percent slopes | 29K | Excessively drained | A | Not limited | Very limited |
| Bloomfield fine sand, 1 to 7 percent slopes | 20K | Somewhat excessively drained | A | Not limited | Very limited |
| Sparta loamy sand, Illinois till plain, 2 to 6 percent slopes | 19K | Excessively drained | A | Not limited | Very limited |
| Water | 17K | Not rated | Not rated | ||
| Onarga sandy loam, 0 to 2 percent slopes | 16K | Well drained | A | Not limited | Very limited |
| Marshan loam, 0 to 2 percent slopes | 14K | Poorly drained | B/D | Very limited | Very limited |
| Udolpho fine sandy loam, 0 to 2 percent slopes | 14K | Poorly drained | B/D | Very limited | Very limited |
| Ridgeville sandy loam, 0 to 2 percent slopes | 12K | Somewhat poorly drained | A/D | Very limited | Very limited |
| Plainfield sand, 7 to 15 percent slopes | 12K | Excessively drained | A | Somewhat limited | Very limited |
| Ade loamy fine sand, 1 to 6 percent slopes | 12K | Somewhat excessively drained | A | Not limited | Very limited |
| Dakota fine sandy loam, 0 to 2 percent slopes | 11K | Well drained | B | Not limited | Very limited |
| Disco sandy loam, 0 to 2 percent slopes | 10K | Well drained | A | Not limited | Very limited |
| Dockery silt loam, 0 to 2 percent slopes, frequently flooded, long duration | 10K | Somewhat poorly drained | B/D | Very limited | Very limited |
| Selma loam, 0 to 2 percent slopes | 9K | Poorly drained | B/D | Very limited | Very limited |
| Edgington silt loam, 0 to 2 percent slopes | 8K | Poorly drained | C/D | Very limited | Very limited |
| Onarga sandy loam, 2 to 5 percent slopes | 7K | Well drained | A | Not limited | Very limited |
| Gilford fine sandy loam, 0 to 2 percent slopes | 7K | Poorly drained | A/D | Very limited | Very limited |
| Harpster silty clay loam, 0 to 2 percent slopes | 7K | Poorly drained | B/D | Very limited | Very limited |
| Broadwell silt loam, 2 to 5 percent slopes | 7K | Well drained | B | Somewhat limited | Very limited |
| Tama silt loam, 2 to 5 percent slopes | 7K | Well drained | B | Somewhat limited | Somewhat 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 43% of soils have significant building limitations, while the rest are generally suitable. Check specific sites carefully — conditions vary across the area.
Septic Systems
About 90% of soils are rated "very limited" for septic absorption fields. The well-drained soils may actually drain too fast for standard leach fields, allowing effluent to reach groundwater. Engineered or alternative systems are frequently required. Always get a professional perc test before purchasing land that needs septic.
Gardening & Agriculture
Soils tend to drain very quickly, meaning nutrients and water don't stick around long. Raised beds with amended soil, drip irrigation, and heavy mulching will give the best results. Compost is your best friend here — it improves water retention dramatically.