Enter any address in Williamson County, Illinois to see its FEMA flood zone
Flash flooding from severe thunderstorms is the dominant flood character in Williamson County, IL. Over the past 30 years, NOAA Storm Events data shows 40 recorded flash flood events and 28 general flood events. Recent examples include flash flooding on May 8, 2024, and general flooding on May 26, 2024, both associated with significant severe weather outbreaks.
National Flood Insurance Program (NFIP) claims data indicates that properties in Zone A, which typically have a Base Flood Elevation (BFE) defined, have experienced the highest number of claims (123) with an average payout of $9,428 and an average water depth of 1.7 feet. However, properties in Zone X, though fewer in number (12 claims), have seen the highest average payouts ($18,343) and an average water depth of 1.2 feet. Properties in Zone X_SHADED have also experienced significant water depth, averaging 3.0 feet with 6 claims.
Homeowners in areas designated as Zone A, as well as those in any flood zone with a history of claims and water intrusion, should pay close attention to flood risk. Given the prevalence of flash flooding, properties in low-lying areas or those near drainage paths are also at higher risk.
Summary generated from NOAA storm narratives and NFIP claim data for this county. Not predictive.
32 NOAA storm reports from this county describe what happened, in the words of the meteorologists who were there.
Williamson County, Illinois has recorded 68 flood-related events since 1996 according to NOAA's Storm Events Database, including 40 flash floods and 28 river or area floods. The county has received 9 federal disaster declarations. Enter any address above to check its FEMA flood zone designation.
FEMA Disaster Declarations (1982–2020)
Source: OpenFEMA Disaster Declarations Summaries.
| Declaration | Type | Date |
|---|---|---|
| Covid-19 | Biological | Jan 20, 2020 |
| Covid-19 Pandemic | Biological | Jan 20, 2020 |
| Severe Storms And Flooding | Severe Storm | Apr 19, 2011 |
| Severe Storms, Flooding, And Tornadoes | Severe Storm | May 8, 2009 |
| Hurricane Katrina Evacuation | Hurricane | Aug 29, 2005 |
| Record/near Record Snow | Snowstorm | Dec 21, 2004 |
| Severe Storms, Tornadoes And Flooding | Tornado | Apr 21, 2002 |
| Severe Storms And Flooding | Severe Storm | Apr 28, 1996 |
| Severe Storms & Tornadoes | Tornado | Jun 5, 1982 |
NOAA Storm Events Database (1996–2025)
Source: NOAA National Weather Service Storm Events Database.
| Type | Date | Damage |
|---|---|---|
| Flash Flood | Jul 19, 2025 | 0.00K |
| Flood | May 26, 2024 | 0.00K |
| Flood | May 14, 2024 | 0.00K |
| Flash Flood | May 8, 2024 | 0.00K |
| Flood | Mar 24, 2023 | 0.00K |
| Flash Flood | Jul 19, 2023 | 25.00K |
| Flood | Mar 3, 2023 | 0.00K |
| Flood | Mar 30, 2022 | 0.00K |
| Flash Flood | Feb 17, 2022 | 0.00K |
| Flash Flood | Aug 4, 2022 | 100.00K |
Flash Flood — Jul 19, 2025
As high pressure slowly crept northward towards the Quad State region, ridging remained over the middle Mississippi River Valley. A slow-moving MCS moved through the northeastern half of the Quad State midday to near sunset. CAPE rose to 1000-2000J/kg in northern portions of Southern Illinois with effective bulk shear around 30kts. Extremely high moisture content with precipitable water values ...
Flood — May 26, 2024
The second major severe weather outbreak for the month occurred on the 26th for the Quad State region. On the synoptic scale, a shortwave trough centered in the middle of the country with a 60 kt mid-level jet moved across northern Arkansas. A weak surface low was moving into SE Missouri during the morning with a secondary low located further northwest. A warm frontal boundary was draped across...
Flood — May 14, 2024
Surface low pressure was drifting across the Quad State on the 14th. Showers and thunderstorms popped up in the afternoon to evening hours with the strongest storm in Southern Illinois moving through Marion, producing damage to vinyl fencing and minor street flooding. CAPE values around 1000 J/kg dropped off after sunset. Lapse rates were meager, around 6 C/km, and shear was also limited to aro...
Flash Flood — May 8, 2024
A major outbreak of severe weather occurred on the 8th for the Quad State region. On the synoptic scale, a longwave trough was centered across the Rockies with deep-layer southwesterly flow from the Southern Plains to the Ohio Valley. A 110 kt upper jet extended from northern KS to IA while a 60 kt mid-level jet was positioned across northern MZ into IA. Surface low pressure near the MZ/KS bord...
Flood — Mar 24, 2023
A nearly stationary front draped itself from central Texas northeast through the Ohio River Valley and produced multiple rounds of showers and thunderstorms, some with very heavy rainfall. Scattered showers and thunderstorms resulted in several cases of flooding or flash flooding. One to three inches of rain fell across the region with isolated higher amounts before the front passed east on the...
Source: NOAA National Weather Service Storm Events Database.
Source: OpenFEMA NFIP Individual Claims (2.25M records analyzed).
FEMA assigns flood zone designations to areas in Williamson County, Illinois:
AE High Risk — 1% annual chance of flooding. Insurance required.
VE Very High Risk — Coastal flooding with wave action.
X (Shaded) Moderate Risk — 500-year floodplain.
X Low Risk — Outside major floodplains.
Properties in Williamson County, Illinois that are in FEMA-designated Special Flood Hazard Areas (zones A and V) with federally backed mortgages are required to carry flood insurance.
Even outside high-risk zones, flood insurance is recommended. From 2014 to 2024, nearly one-third of NFIP claims came from outside the high-risk Special Flood Hazard Area.
Visit FloodSmart.gov to find an agent and get a quote.