Cook County, Illinois
The dominant drainage class is Moderately well drained and the dominant hydrologic group is D (very slow infiltration, high 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 Cook County, Illinois.
| Soil Map Unit | Acres | Drainage | Hydro Group | Dwellings | Septic |
|---|---|---|---|---|---|
| Urban land | 105K | Not rated | Not rated | ||
| Orthents, clayey, undulating | 55K | Moderately well drained | D | Very limited | Very limited |
| Urban land-Orthents, clayey, complex, nearly level | 31K | Not rated | Not rated | ||
| Urban land-Anthroportic Udorthents complex, 0 to 2 percent slopes | 27K | Not rated | Not rated | ||
| Urban land-Orthents, loamy, complex, nearly level | 27K | Not rated | Not rated | ||
| Anthroportic Udorthents-Urban land-Elliott complex, 0 to 2 percent slopes | 22K | Moderately well drained | D | Somewhat limited | Very limited |
| Ashkum silty clay loam, 0 to 2 percent slopes | 20K | Poorly drained | C/D | Very limited | Very limited |
| Milford silty clay loam, 0 to 2 percent slopes | 18K | Poorly drained | C/D | Very limited | Very limited |
| Markham-Ashkum-Beecher complex, 1 to 6 percent slopes | 17K | Moderately well drained | C/D | Very limited | Very limited |
| Markham silt loam, 2 to 4 percent slopes | 16K | Moderately well drained | C | Very limited | Very limited |
| Markham silt loam, 4 to 6 percent slopes, eroded | 14K | Moderately well drained | C | Very limited | Very limited |
| Water | 13K | Not rated | Not rated | ||
| Orthents, loamy, 1 to 6 percent slopes | 13K | Well drained | C | Somewhat limited | Very limited |
| Ozaukee silt loam, 2 to 4 percent slopes | 10K | Moderately well drained | C | Very limited | Very limited |
| Ozaukee silt loam, 4 to 6 percent slopes, eroded | 9K | Moderately well drained | C | Somewhat limited | Very limited |
| Anthroportic Udorthents-Urban land-Elliott complex, 2 to 4 percent slopes | 9K | Moderately well drained | D | Somewhat limited | Very limited |
| Ozaukee silt loam, 6 to 12 percent slopes, eroded | 8K | Moderately well drained | C | Somewhat limited | Very limited |
| Frankfort silt loam, 2 to 4 percent slopes | 7K | Somewhat poorly drained | D | Very limited | Very limited |
| Sawmill silty clay loam, heavy till plain, 0 to 2 percent slopes, frequently flooded | 7K | Poorly drained | B/D | Very limited | Very limited |
| Milford-Martinton complex, 0 to 2 percent slopes | 7K | Poorly drained | C/D | Very limited | Very limited |
What This Means
Building & Foundations
About 39% of soils have significant building limitations, while the rest are generally suitable. Check specific sites carefully — conditions vary across the area.
Septic Systems
About 53% 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
Drainage is generally favorable for gardening. Adding compost and mulch will improve fertility and water retention. Test your soil's pH before planting — most vegetables prefer 6.0-7.0.