Soil types in Illinois

What this means

What Illinois soils mean for gardens, lawns and septic systems

For gardens

Typical topsoil in Illinois is slightly acidic: pH 6.5 (most land between 5.8 and 7.0), the range most vegetables, flowers and lawn grasses prefer.

Loamy topsoil (loam, silt loam and similar) covers 94% of the land: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silt loam (66% of the land).

58% of the land is somewhat poorly to very poorly drained, so soil stays soggy for long spells after rain and in wet seasons. Raised beds, plants that tolerate wet feet, and not working the soil while wet all help.

For lawns and yards

On 74% of the land, rain soaks in slowly (hydrologic groups C and D, including dual groups that are D until drained). Expect runoff and puddles after heavy rain: core-aerate compacted lawns and keep ground sloping away from foundations.

A seasonal high water table comes within 18 inches of the surface on 54% of the land, often in spring. Basements, sump pumps and lawns in low spots feel it first.

For septic systems

For conventional septic absorption fields, NRCS rates 85% of the land in Illinois very limited, 13% somewhat limited and 0% not limited (2% 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.

Flooding is mapped on 13% of the land (4% occasional, 8% frequent).

Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.

Generated from the mapped numbers above using fixed rules, not a site visit. See how these notes are written.