Illinois / Pope County
Score 31 · moderate · #87 of 102 in IL
Crawl space moisture in Pope County, IL
Pope County scores moderate: no single wet-soil signal dominates its mapped acres. Where a seasonal water table is reported — 67% of acres — it averages 2.3 ft below grade.
- 1Water table 2.3 ft
- 2Wet soils 11%
- 3Moisture score 31
- 4EPA radon zone 2
Reading the Pope County soil survey
The score of 31 combines four parts, each from the USDA survey: wet drainage classes contribute 27.9 points of 100 on their own scale, group D soils 30.1, a shallow water table 43.9, and flooding 14.9; the weights are on the methodology page. The dominant hydrologic group is C (55% of acres): slow infiltration (clay layers).
At 2.3 ft the seasonal water table is usually below a crawl-space floor, but the 67% of acres that report one are by definition the wettest parts of the county; on those lots, a wet spring can bring water close to the footings.
Pope County against the rest of Illinois
Pope County ranks 87 of 102 Illinois counties, 18 points below the state median of 49. That places it in the middle range, nationally and for the state. Statewide, 57% of mapped soil is in the wet drainage classes; here it is 11%, below the state figure — the score here comes from a shallow water table rather than drainage class alone. After moderately well drained, the next most common class is well drained at 32%.
Flooding. 2.9% of acres with a flooding class are rated frequent; 17.9% of acres with a flooding class are rated occasional; 6.2% of acres with a flooding class are rated rare. That is a large flood-prone share; a crawl space in the floodplain needs flood vents under most local floodplain ordinances, which is a separate rule from R408 and can rule out a fully sealed design.
What it means for a crawl space here
In a moderate county the soil record is mixed rather than uniformly wet, so conditions vary from lot to lot. Where the lot drains, the model-code default — a vented crawl space with 1 sq ft of net vent per 150 sq ft of floor, or 1 per 1500 with a Class I vapor retarder on the ground — is a reasonable starting point; where the sections above point to a shallow water table or flood-prone soil on your lot, plan as for an elevated county. Either way, check the site first: grading that falls away from the foundation, gutters and downspouts that discharge well clear of it, and a ground cover over bare earth. A wet crawl space in a moderate county points to one of those first.
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 Pope County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area IL151; drainage covers 98% of 239,765 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.