Soil series profile

Keomah soil series

Keomah is a somewhat poorly drained soil with a silt loam surface, mapped on 301,119 acres in 63 counties across 2 states. Hydrologic group C/D.

#1131 by mapped area fine Aeric Endoaqualfs (Alfisols)

Drainage class
Somewhat poorly drained
100% of mapped acres
Hydrologic group
C/D
>99% of mapped acres
Typical topsoil pH
6.5
slightly acidic · range 6.2–7.2
Mapped area
301k
acres in 63 counties, 2 states

Typical Keomah profile

Texture and pH by depth

Typical Keomah soil profile by depth 0 in 10 in 20 in 30 in 40 in 50 in 0–6 in · Ap · pH 6.5 · 16% clay Silt loam 6–13 in · E · pH 5.7 · 20% clay Silt loam 13–28 in · Bt · pH 5.2 · 38% clay Silty clay loam 28–48 in · Btg · pH 6.0 · 35% clay Silty clay loam 48–60 in · Cg · pH 6.5 · 24% clay Silt loam
Depth to scale. More strongly shaded layers hold more clay. Horizon names are the soil survey's (A = topsoil, B = subsoil, C = parent material).
Show as a table
Typical Keomah horizons (representative values)
Depth Texture pH Clay Sand Organic matter
0–6 in (Ap) Silt loam 6.5 16% 4% 2%
6–13 in (E) Silt loam 5.7 20% 4% 0.65%
13–28 in (Bt) Silty clay loam 5.2 38% 2% 0.5%
28–48 in (Btg) Silty clay loam 6.0 35% 1% 0.3%
48–60 in (Cg) Silt loam 6.5 24% 3% 0.1%

Representative values from the most extensive Keomah map unit (Keomah silt loam, 0 to 2 percent slopes, survey area IL117). Other map units of this series vary within the series range.

Hands holding dark garden soil
Stock photo for illustration, not a sample of this soil series. Credit on the Sources & method page.

What this means

What Keomah soil means for gardens, lawns and septic systems

For gardens

Typical topsoil in Keomah soils is slightly acidic: pH 6.5 (most land between 6.2 and 7.2), the range most vegetables, flowers and lawn grasses prefer.

Loamy topsoil (loam, silt loam and similar) covers >99% of mapped Keomah acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silt loam (>99% of mapped Keomah acres).

100% of mapped Keomah acres 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 >99% of mapped acres, 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 100% of mapped acres, often in spring. Basements, sump pumps and lawns in low spots feel it first.

For a septic system

For conventional septic absorption fields, NRCS rates >99% of the acres in mapped Keomah soils very limited, 0% somewhat limited and 0% not limited.

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.

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

Where Keomah soil is found

Mapped acres

Keomah is mapped in Illinois and Iowa. The 60 counties with the most Keomah acres:

Counties with the most mapped Keomah soil
County Acres Share of county land
Adams County, IL 28,700 5.5%
Schuyler County, IL 25,731 9.5%
Macoupin County, IL 23,310 4.2%
Fulton County, IL 22,342 4.2%
Peoria County, IL 21,904 5.7%
Greene County, IL 19,926 5.8%
McDonough County, IL 18,790 5.0%
Hancock County, IL 17,904 3.6%
Brown County, IL 16,687 8.8%
Woodford County, IL 9,718 2.9%
Sangamon County, IL 9,675 1.8%
Morgan County, IL 8,600 2.4%
Des Moines County, IA 7,733 2.9%
Knox County, IL 6,524 1.4%
Christian County, IL 4,737 1.0%
Logan County, IL 4,729 1.2%
Scott County, IL 4,469 2.9%
Lee County, IA 4,384 1.3%
Cass County, IL 3,340 1.4%
Marshall County, IL 3,241 1.3%
Pike County, IL 3,143 0.6%
De Witt County, IL 3,076 1.2%
Warren County, IL 2,650 0.8%
Menard County, IL 2,572 1.3%
Vermilion County, IL 2,164 0.4%
Louisa County, IA 2,137 0.8%
Stark County, IL 2,001 1.1%
McLean County, IL 1,903 0.3%
Washington County, IA 1,821 0.5%
Mercer County, IL 1,792 0.5%
Henry County, IA 1,744 0.6%
Rock Island County, IL 1,728 0.7%
Jersey County, IL 1,721 0.7%
Tazewell County, IL 1,498 0.4%
Stephenson County, IL 1,117 0.3%
Henry County, IL 1,038 0.2%
Ogle County, IL 863 0.2%
Bureau County, IL 785 0.1%
Jo Daviess County, IL 695 0.2%
Jefferson County, IA 694 0.2%
Whiteside County, IL 518 0.1%
Keokuk County, IA 513 0.1%
Henderson County, IL 362 0.2%
Carroll County, IL 346 0.1%
Winnebago County, IL 318 0.1%
Lee County, IL 200 0.0%
Iowa County, IA 187 0.1%
Putnam County, IL 181 0.2%
Mahaska County, IA 165 0.0%
Johnson County, IA 105 0.0%
Marion County, IA 101 0.0%
Mason County, IL 100 0.0%
Madison County, IA 89 0.0%
Boone County, IL 74 0.0%
LaSalle County, IL 71 0.0%
Van Buren County, IA 59 0.0%
Wapello County, IA 38 0.0%
Warren County, IA 30 0.0%
Dallas County, IA 30 0.0%
Davis County, IA 18 0.0%

Septic absorption fields

NRCS rating, share of Keomah acres

Not limited 0%
Somewhat limited 0%
Very limited >99%
Not rated <1%
Septic tank absorption field rating across mapped Keomah acres. Scale 0 to 100% of mapped land.
Show as a table
Septic tank absorption field rating across mapped Keomah acres.
CategoryShare of acres
Not limited0.0%
Somewhat limited0.0%
Very limited99.9%
Not rated0.1%

Drainage, water table and flooding

Share of Keomah acres

Depth to seasonal high water table
About 1.2 feet (14 in) (median where reported); within 18 inches on 100% of acres.
Flooding
Not mapped as flooding on most acres.
Slope
Typically 1–4% (median 1%).
Topsoil organic matter
Median 2%.

Drainage class

Excessively drained 0%
Somewhat excessively drained 0%
Well drained 0%
Moderately well drained 0%
Somewhat poorly drained 100%
Poorly drained 0%
Very poorly drained 0%
Drainage class across mapped Keomah acres. Scale 0 to 100% of mapped land.
Show as a table
Drainage class across mapped Keomah acres.
CategoryShare of acres
Excessively drained0.0%
Somewhat excessively drained0.0%
Well drained0.0%
Moderately well drained0.0%
Somewhat poorly drained100.0%
Poorly drained0.0%
Very poorly drained0.0%

Hydrologic soil group

A: fast infiltration (mostly sandy or gravelly) 0%
B: moderate infiltration 0%
C: slow infiltration 0%
D: very slow infiltration (clayey, shallow or wet) 0%
A/D: D as is, A if drained 0%
B/D: D as is, B if drained 0%
C/D: D as is, C if drained >99%
Not rated <1%
Hydrologic soil group across mapped Keomah acres. Scale 0 to 100% of mapped land.
Show as a table
Hydrologic soil group across mapped Keomah acres.
CategoryShare of acres
A: fast infiltration (mostly sandy or gravelly)0.0%
B: moderate infiltration0.0%
C: slow infiltration0.0%
D: very slow infiltration (clayey, shallow or wet)0.0%
A/D: D as is, A if drained0.0%
B/D: D as is, B if drained0.0%
C/D: D as is, C if drained99.9%
Not rated0.1%

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 Keomah (component kind "Series") in SSURGO: 301,119 acres.
Method
Shares are by mapped acres of Keomah components. The profile comes from the single largest Keomah component. Full methodology.

Independent reference site. No government affiliation or endorsement.

Full narrative description: USDA Official Soil Series Description for Keomah.