States / Mississippi
82 counties · median score 35
Crawl space moisture in Mississippi
Mississippi is mixed: 29 of 82 counties score high or elevated, concentrated where drainage is poorest — Humphreys County tops the list at 86 — while Tishomingo County scores just 12. Where you are in the state matters more than the state itself.
- 1Wettest county Humphreys County
- 2High or elevated 29 of 82
- 3Median score 35
- 4Driest county Tishomingo County
Mississippi's soil, taken as a whole
Across the 30,533,290 acres mapped in these 82 counties, 35% of soil with a drainage class is somewhat poorly, poorly or very poorly drained, and 64% of acres report a seasonal water table within about two metres. That is a wet state by any measure; a third or more of its land holds water near the surface for part of the year. 82 of the 82 counties have mapped soils subject to occasional or frequent flooding.
| Drainage class | Share of mapped acres |
|---|---|
| Excessively drained | 0.6% |
| Somewhat excessively drained | 0.7% |
| Well drained | 38% |
| Moderately well drained | 26.2% |
| Somewhat poorly drained | 17.8% |
| Poorly drained | 14.2% |
| Very poorly drained | 2.5% |
Radon. By EPA zone, 0 Mississippi counties here are zone 1 (highest potential), 8 zone 2 and 74 zone 3. EPA says to test regardless of zone; a sealed crawl space is the cheapest moment to add radon venting if a test calls for it.
Every Mississippi county
Sorted wettest first. High and elevated counties link to their own page with the full soil breakdown.
What drives the Mississippi numbers
The wettest county, Humphreys County, is 79% poorly drained by dominant condition, with a seasonal water table averaging 1.2 ft below grade across the 95% of acres that report one, and sits in EPA radon zone 3. The driest, Tishomingo County, is 77% well drained. 10 Mississippi counties reach the high tier, where poorly drained soils, group D clays and a shallow water table occur together.
The score is a guide to the soil, not to a house: a well-graded lot with working gutters in a high county can have a dry crawl space, and a bad downspout can flood one in a low county. The R408 calculator sizes venting or encapsulation for any footprint.
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted; EPA Map of Radon Zones, county table (June 2024 JSON). Checked 2026-10-23.