Illinois / Cumberland County
Score 58 · elevated · #18 of 102 in IL
Crawl space moisture in Cumberland County, IL
74% of Cumberland County's mapped soil is somewhat poorly to very poorly drained, which means ground that stays wet near the surface for significant periods. Where a seasonal water table is reported — 84% of acres — it averages 1.1 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1.1 ft
- 2Wet soils 74%
- 3Moisture score 58
- 4EPA radon zone 2
Reading the Cumberland County soil survey
The score of 58 combines four parts, each from the USDA survey: wet drainage classes contribute 66.6 points of 100 on their own scale, group D soils 49.2, a shallow water table 70.2, and flooding 10.9; the weights are on the methodology page. The dominant hydrologic group is C/D (59% of acres): D when undrained, C when drained.
A water table under two feet is the single most important number here. A crawl-space floor is usually 18 to 36 inches below the joists and often below outside grade, so in a wet season groundwater can stand at or above the crawl-space floor across much of Cumberland County. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Cumberland County against the rest of Illinois
Cumberland County ranks 18 of 102 Illinois counties, 9 points above the state median of 49. That puts it in the wettest quarter of the state. Statewide, 57% of mapped soil is in the wet drainage classes; here it is 74%. After poorly drained, the next most common class is somewhat poorly drained at 30%.
Flooding. 10.6% of acres with a flooding class are rated frequent; 1.1% of acres with a flooding class are rated rare. Flood-prone soils are a minority here, concentrated along streams; the score mostly reflects what happens between floods.
What it means for a crawl space here
In an elevated county the soil supplies more moisture than average, but a vented crawl space can work if the ground is covered: the code lets vent area drop from 1 sq ft per 150 to 1 per 1500 with a Class I vapor retarder on the ground, which is an admission of how much moisture comes from below. Grading, gutters and a ground cover usually decide whether a crawl space here stays dry before any decision about sealing it.
Radon. EPA radon zone 2. The zone is a county-level prediction; EPA says elevated levels occur in every zone and every home should be tested.
Near Cumberland County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area IL035; drainage covers 99% of 221,620 mapped acres); EPA Map of Radon Zones, county table (June 2024 JSON); IRC R408.3 Unvented crawl space, as adopted in S.C. Code Regs. 8-1221 (LII). Checked 2026-10-23.