HomeSoil seriesOsco
Osco soil series
Osco soils cover 1,068,357 mapped acres, almost all of them in Illinois. USDA rates shrink-swell a limit for houses without basements on 29% of that land, and a shallow water table a limit for basements on 3%.
It is the leading soil series by area in 8 of the counties and cities on this site, including Warren County, IL; Carroll County, IL; Knox County, IL.
SSURGO survey versions to August 5, 2026 · series description revised 2011-02
of its land: shrink-swell limits houses without basements
of its land: a shallow water table limits basements
median highest linear extensibility (6% and up is high)
median highest clay content in the top 150 cm
USDA's description
The Osco series consists of very deep, well drained soils formed in loess. These soils are on crests and shoulders of hills on loess covered till plains and on treads and risers of stream terraces in river valleys. Slope ranges from 0 to 18 percent. The mean annual precipitation is about 890 mm (35 inches), and the mean annual air temperature is about 8.3 degrees C (47 degrees F).
Source: USDA NRCS series description (OSD) for Osco, revised 2011-02. Read it.
Engineering properties
| Mapped area (SSURGO) | 1,068,357 acres |
| Shrink-swell limits houses without basements | 28.7% |
| Shallow water table limits basements | 2.9% |
| Very limited for septic absorption fields | 2.9% |
| Most common drainage class | Well drained |
| Most common hydrologic soil group | B |
| Taxonomic class | Fine-silty, mixed, superactive, mesic Typic Argiudolls |
| Type location | Carroll County, Illinois |
Where Osco is mapped
| State | Mapped acres |
|---|---|
| Illinois | 1,037,197 |
| Iowa | 29,553 |
| Minnesota | 1,607 |
Places where Osco leads
Counties and cities where Osco covers more mapped land than any other series.
| Place | Share of mapped land |
|---|---|
| Warren County, IL | 26% |
| Carroll County, IL | 25% |
| Knox County, IL | 23% |
| Stark County, IL | 18% |
| Ogle County, IL | 15% |
| Stephenson County, IL | 12% |
| Bureau County, IL | 12% |
| Henry County, IL | 12% |
Other places where Osco is a main soil
Counties and cities where Osco is among the six soil series covering the most mapped land, but not the first. Share of the place's mapped land.
Counties
Sources
Shares and properties: USDA NRCS SSURGO via Soil Data Access, weighted by each component's share of its map units. Description: the USDA NRCS series description. How we count.