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Rock Island County, Illinois

A shallow water table limits basements on 32% of Rock Island County's mapped land, a higher share than 51% of US counties. Shrink-swell clay limits houses without basements on 6%.

None of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 240 flood losses here since 2016, 35% of them in buildings with basements. 76% of homes were built before 1980, against 50% nationally; the median home dates from 1962.

Data as of October 13, 2026 · sources

6%

expansive clay: shrink-swell limits slab homes

32%

high water table: limits basements

0%

in drought, October 13, 2026

76%

of homes built before 1980

Soil under Rock Island County

Expansive clay (limits slab homes)6.0%
High water table (limits basements)31.6%
Septic fields very limited55.8%
Clay swell (LEP, by area)3.7%
High-swell land (LEP 6%+)3.0%
Mapped soil288,910 acres
Soil seriesShare hereSeries nationally: high water table
Fayette14%0%
Sylvan9%n/a
Hickory8%n/a
Muscatune5%n/a
Sawmill5%n/a
Osco4%3%
Scott County: 41%Mercer County: 44%Henry County: 48%Muscatine County: 50%Clinton County: 44%Cedar County: 43%Whiteside County: 40%Louisa County: 70%Rock Island County ScottMercerHenryMuscatineClintonCedarWhitesideLouisaRock Island
Rock Island County (heavy outline) and nearby counties, shaded by high water table share.under 10%10-25%25-40%40-60%60%+

How we count · survey areas IL161 (2025-08-31)

What the numbers mean here

On 32% of Rock Island County's mapped land, soil stays saturated within about 6 feet of the surface for part of the year, which is basement depth.

Rain over the 12 months to August 2026: 34.50 in, 3.16 in below the 1991-2020 average year of 37.66 in.

USDA rates 56% of the land very limited for septic absorption fields.

Drought

0% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 19 of the last 52 weeks; the most was 100% of its area, in 14 weeks, most recently on the March 31, 2026 map.

October 21, 2025Share of area in drought, weeklyOctober 13, 2026
Category, October 13, 2026Share of county
D0 abnormally dry or worse0%
D1 moderate drought or worse0%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

240 flood losses since 2016, $4.0 million paid. The worst year was 2019, with 128. Foundations of the buildings, where recorded: 35% basements, 6% slabs, 8% crawl spaces, 52% elevated. Median water depth outside the building: 22 in.

YearFlood losses
20169
201725
201822
2019128
20208
20210
20220
202329
202410
20255
2026 to date4

Rain

Average year, 1991-202037.66 in
12 months to August 202634.50 in (-3.16)
202533.23 in (-4.43)
Wettest year since 18952009: 50.79 in
Driest year since 18952005: 19.98 in
Days with 1 inch or more, normal at MOLINE QUAD CITY INTL AP (3 mi away)9.6

Homes

Housing units66,759
Median year built1962
Built before 198076%
Built 2000 or later10%
Owner-occupied70%
Median value, owner-occupied$150,400
Single-family detached70%

What repairs cost

Published ranges from cost guides, not quotes. More sources, and where they disagree.

WorkRangeSource
Basement waterproofing, US $3,000 to $10,000 Fixr, February 6, 2026
Sump pump installation, US $800 to $2,000 Fixr, January 31, 2025
Crawl space encapsulation, US $2,000 to $8,000 Fixr, August 29, 2025

Nearby counties

PlaceDistanceExpansive clayHigh water table
Scott County, IA 12 mi 36% 41%
Mercer County, IL 20 mi 15% 44%
Henry County, IL 24 mi 19% 48%
Muscatine County, IA 28 mi 20% 50%
Clinton County, IA 30 mi 15% 44%
Cedar County, IA 36 mi 39% 43%
Whiteside County, IL 39 mi 2% 40%
Louisa County, IA 40 mi 38% 70%

Sources: USDA SSURGO (August 31, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status