Soil series profile
Belknap soil series
Belknap is a somewhat poorly drained soil with a silt loam surface, mapped on 637,595 acres in 71 counties across 4 states. Hydrologic group B/D.
- Drainage class
- Somewhat poorly drained >99% of mapped acres
- Hydrologic group
- B/D 81% of mapped acres
- Typical topsoil pH
- 5.9 moderately acidic · range 5.9–5.9
- Mapped area
- 638k acres in 71 counties, 4 states
Typical Belknap profile
Texture and pH by depth
Show as a table
| Depth | Texture | pH | Clay | Sand | Organic matter |
|---|---|---|---|---|---|
| 0–3 in (Ap) | Silt loam | 5.9 | 13% | 9% | 2% |
| 3–9 in (Bw) | Silt loam | 5.0 | 14% | 10% | 0.75% |
| 9–77 in (Bg) | Silt loam | 5.0 | 15% | 11% | 0.5% |
| 77–100 in (BCg) | Silt loam | 5.6 | 17% | 12% | 0.25% |

What this means
What Belknap soil means for gardens, lawns and septic systems
For gardens
Typical topsoil in Belknap soils is moderately acidic: pH 5.9. Many vegetables grow well here, and some gardens benefit from a little lime. Test before adding any.
Loamy topsoil (loam, silt loam and similar) covers 99% of mapped Belknap acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silt loam (99% of mapped Belknap acres).
>99% of mapped Belknap 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 81% 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 Belknap soils very limited, 0% somewhat limited and 0% not limited (1% 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 >99% of the acres (53% occasional, 45% frequent).
Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.
Where Belknap soil is found
Mapped acres
Belknap is mapped in Illinois, Kentucky, Missouri and Indiana. The 60 counties with the most Belknap acres:
| County | Acres | Share of county land |
|---|---|---|
| Hamilton County, IL | 37,167 | 13.4% |
| Hopkins County, KY | 36,134 | 10.4% |
| Jefferson County, IL | 34,530 | 9.7% |
| Daviess County, KY | 34,466 | 11.7% |
| Wayne County, IL | 31,488 | 7.0% |
| Williamson County, IL | 28,667 | 11.0% |
| Franklin County, IL | 26,370 | 10.2% |
| Webster County, KY | 24,906 | 11.6% |
| Saline County, IL | 21,798 | 8.9% |
| Muhlenberg County, KY | 21,488 | 7.2% |
| Henderson County, KY | 20,146 | 7.2% |
| McLean County, KY | 20,134 | 12.4% |
| Audrain County, MO | 20,124 | 4.5% |
| Edwards County, IL | 18,520 | 13.1% |
| Pike County, IN | 18,103 | 8.5% |
| Richland County, IL | 17,794 | 7.8% |
| Perry County, IL | 17,244 | 6.4% |
| White County, IL | 17,128 | 5.6% |
| Massac County, IL | 15,065 | 10.6% |
| Montgomery County, MO | 14,919 | 4.3% |
| Lawrence County, IL | 14,828 | 6.3% |
| Marion County, MO | 14,335 | 5.1% |
| Johnson County, IL | 14,099 | 7.0% |
| Jackson County, IL | 11,122 | 3.1% |
| Pike County, MO | 10,603 | 2.5% |
| Pulaski County, IL | 9,663 | 8.2% |
| Wabash County, IL | 9,296 | 6.5% |
| Caldwell County, KY | 8,445 | 3.8% |
| Hancock County, KY | 8,405 | 6.9% |
| Pope County, IL | 8,377 | 3.9% |
| Ralls County, MO | 7,781 | 2.6% |
| Marion County, IL | 6,035 | 1.7% |
| Clay County, IL | 5,717 | 1.9% |
| Callaway County, MO | 5,383 | 1.0% |
| Gallatin County, IL | 3,442 | 1.7% |
| Hardin County, IL | 2,873 | 2.8% |
| Warren County, MO | 2,838 | 1.0% |
| Alexander County, IL | 2,806 | 2.0% |
| Crittenden County, KY | 2,505 | 1.1% |
| Christian County, KY | 2,376 | 0.5% |
| Fayette County, IL | 974 | 0.2% |
| Warrick County, IN | 941 | 0.4% |
| Washington County, IL | 826 | 0.2% |
| Union County, KY | 802 | 0.4% |
| Ohio County, KY | 703 | 0.2% |
| Macoupin County, IL | 584 | 0.1% |
| Gibson County, IN | 562 | 0.2% |
| Shelby County, IL | 531 | 0.1% |
| Effingham County, IL | 473 | 0.2% |
| Owen County, IN | 446 | 0.2% |
| Montgomery County, IL | 444 | 0.1% |
| Bond County, IL | 391 | 0.2% |
| Madison County, IL | 390 | 0.1% |
| Lewis County, MO | 341 | 0.1% |
| Jasper County, IL | 279 | 0.1% |
| Clinton County, IL | 245 | 0.1% |
| Cumberland County, IL | 244 | 0.1% |
| Randolph County, IL | 232 | 0.1% |
| Clark County, IL | 223 | 0.1% |
| Daviess County, IN | 204 | 0.1% |
Septic absorption fields
NRCS rating, share of Belknap acres
Show as a table
| Category | Share of acres |
|---|---|
| Not limited | 0.0% |
| Somewhat limited | 0.0% |
| Very limited | 98.6% |
| Not rated | 1.4% |
Drainage, water table and flooding
Share of Belknap acres
- Depth to seasonal high water table
- About 1.2 feet (14 in) (median where reported); within 18 inches on 81% of acres.
- Flooding
- Mapped as flooding on >99% of acres (53% occasional, 45% frequent).
- Slope
- Typically 0–1% (median 1%).
- Topsoil organic matter
- Median 2.5%.
Drainage class
Show as a table
| Category | Share of acres |
|---|---|
| Excessively drained | 0.0% |
| Somewhat excessively drained | 0.0% |
| Well drained | 0.0% |
| Moderately well drained | 0.0% |
| Somewhat poorly drained | 99.9% |
| Poorly drained | 0.0% |
| Very poorly drained | 0.0% |
| Not rated | 0.1% |
Hydrologic soil group
Show as a table
| Category | Share of acres |
|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 0.0% |
| B: moderate infiltration | 0.0% |
| C: slow infiltration | 18.1% |
| D: very slow infiltration (clayey, shallow or wet) | 0.0% |
| A/D: D as is, A if drained | 0.0% |
| B/D: D as is, B if drained | 80.5% |
| C/D: D as is, C if drained | 0.0% |
| Not rated | 1.4% |
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 Belknap (component kind "Series") in SSURGO: 637,595 acres.
- Method
- Shares are by mapped acres of Belknap components. The profile comes from the single largest Belknap component. Full methodology.