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Flood in Williamson County, Illinois
68 floods and flash floods events in the NCEI Storm Events record, 1950 to 2026. Event types counted: Flood, Flash Flood, Coastal Flood, Lakeshore Flood.
NCEI notes that Storm Data is compiled from a variety of sources including the National Weather Service, other federal, state and local agencies, the media and the public; that property and crop damage figures are estimates; and that some events are recorded by NWS forecast zone rather than by county. FEMA notes that NFIP claim records are redacted and aggregated to protect the privacy of policyholders. Storm records through 30 Jun 2026.
Williamson County, Illinois, has 68 flood events in the NCEI record since 1950, with at least one in 24 different years.
April is the busiest month, with 14 of the recorded events. The last 20 years account for 40 events against 28 in the 20 years before, a change that reflects reporting practice as much as weather.
The county holds 1% of the 6,507 flood events recorded in Illinois; its 16.2 per 100 square miles compares with 11.7 statewide.
NCEI attributes 1 death in the county to floods and flash floods.
Compared with Illinois
| Measure | Williamson County | Illinois | US |
|---|---|---|---|
| Flood events since 1950 | 68 | 6,507 | 183,559 |
| Per 100 square miles | 16.2 | 11.7 | 5.2 |
| Per 10,000 residents | 10.2 | 5.1 | 5.5 |
| Deaths recorded | 1 | 61 | 2,961 |
| Busiest month | April | June | June |
By year
Seasonality
4Feb
3Mar
7Apr
14May
11Jun
8Jul
8Aug
5Sep
2Oct
0Nov
3Dec
3
Recorded events
All 68 events, most recent first. Magnitude is hail size, tornado rating or wind speed as recorded.
| Date | Event type | Magnitude | Property damage | Crop damage | Deaths | Injuries | Geography |
|---|---|---|---|---|---|---|---|
| 19 Jul 2025 | Flash Flood | — | — | — | — | — | County |
| 26 May 2024 | Flood | — | — | — | — | — | County |
| 14 May 2024 | Flood | — | — | — | — | — | County |
| 8 May 2024 | Flash Flood | — | — | — | — | — | County |
| 19 Jul 2023 | Flash Flood | — | $25K | — | — | — | County |
| 24 Mar 2023 | Flood | — | — | — | — | — | County |
| 3 Mar 2023 | Flood | — | — | — | — | — | County |
| 4 Aug 2022 | Flash Flood | — | $100K | — | — | — | County |
| 30 Mar 2022 | Flood | — | — | — | — | — | County |
| 17 Feb 2022 | Flash Flood | — | — | — | — | — | County |
| 11 Mar 2021 | Flash Flood | — | $5K | — | — | — | County |
| 1 Jul 2020 | Flash Flood | — | — | — | — | — | County |
| 22 Jun 2019 | Flash Flood | — | — | — | — | — | County |
| 21 Jun 2019 | Flash Flood | — | — | — | — | — | County |
| 24 Apr 2019 | Flood | — | — | — | — | — | County |
| 15 Jul 2018 | Flash Flood | — | $10K | — | — | — | County |
| 24 Feb 2018 | Flash Flood | — | — | — | — | — | County |
| 21 Feb 2018 | Flood | — | — | — | — | — | County |
| 5 Nov 2017 | Flood | — | — | — | — | — | County |
| 13 Jul 2017 | Flood | — | — | — | — | — | County |
| 30 Apr 2017 | Flash Flood | — | $30K | — | — | — | County |
| 29 Apr 2017 | Flood | — | $40K | — | — | — | County |
| 29 Apr 2017 | Flash Flood | — | $50K | — | — | — | County |
| 14 Aug 2016 | Flash Flood | — | — | — | — | — | County |
| 13 Aug 2016 | Flash Flood | — | — | — | — | — | County |
| 6 Jul 2016 | Flood | — | — | — | — | — | County |
| 11 May 2016 | Flash Flood | — | — | — | — | — | County |
| 19 Jun 2015 | Flash Flood | — | — | — | — | — | County |
| 4 Apr 2014 | Flood | — | — | — | — | — | County |
| 3 Apr 2014 | Flash Flood | — | $5K | — | — | — | County |
| 3 Apr 2014 | Flash Flood | — | — | — | — | — | County |
| 21 Dec 2013 | Flash Flood | — | — | — | — | — | County |
| 1 Sep 2012 | Flood | — | — | — | — | — | County |
| 1 May 2011 | Flood | — | $75K | — | — | — | County |
| 1 May 2011 | Flood | — | $30K | — | — | — | County |
| 24 Apr 2011 | Flood | — | — | — | — | — | County |
| 23 Apr 2011 | Flash Flood | — | — | — | — | — | County |
| 3 Apr 2008 | Flash Flood | — | — | — | — | — | County |
| 31 Mar 2008 | Flash Flood | — | — | — | — | — | County |
| 18 Mar 2008 | Flood | — | $375K | — | — | — | County |
| 4 Jul 2006 | Flash Flood | — | $2K | — | — | — | County |
| 9 Mar 2006 | Flash Flood | — | — | — | — | — | County |
| 15 Nov 2005 | Flash Flood | — | $4K | — | — | — | County |
| 15 Nov 2005 | Flash Flood | — | $10K | — | — | — | County |
| 17 Dec 2001 | Flash Flood | — | $10K | — | — | — | County |
| 17 Dec 2001 | Flood | — | — | — | — | — | Forecast zone |
| 18 Sep 2001 | Flood | — | — | — | — | — | County |
| 9 Aug 2001 | Flash Flood | — | — | — | — | — | County |
| 3 Aug 2000 | Flood | — | — | — | 1 | — | County |
| 17 Jun 2000 | Flash Flood | — | — | — | — | — | County |
| 17 Jun 2000 | Flood | — | — | — | — | — | Forecast zone |
| 16 Jun 2000 | Flash Flood | — | — | — | — | — | County |
| 22 May 2000 | Flood | — | — | — | — | — | County |
| 18 May 2000 | Flash Flood | — | — | — | — | — | County |
| 3 Jan 2000 | Flood | — | — | — | — | — | County |
| 22 Jan 1999 | Flash Flood | — | — | — | — | — | County |
| 21 Jan 1999 | Flash Flood | — | $70K | — | — | — | County |
| 29 Jun 1998 | Flash Flood | — | $50K | — | — | — | County |
| 15 Apr 1998 | Flash Flood | — | $40K | — | — | — | County |
| 19 Jul 1997 | Flood | — | — | — | — | — | County |
| 21 Jan 1997 | Flood | — | — | — | — | — | Forecast zone |
| 8 Jun 1996 | Flood | — | — | — | — | — | County |
| 10 May 1996 | Flash Flood | — | $1.0M | — | — | — | County |
| 5 May 1996 | Flash Flood | — | — | — | — | — | County |
| 1 May 1996 | Flood | — | — | — | — | — | Forecast zone |
| 28 Apr 1996 | Flash Flood | — | $500K | $50K | — | — | County |
| 22 Apr 1996 | Flash Flood | — | — | — | — | — | County |
| 22 Apr 1996 | Flood | — | — | — | — | — | Forecast zone |
Questions and answers
How many flood events has Williamson County had?
68 events in the NCEI Storm Events record between 1950 and 2026. Reporting of floods and flash floods became far more complete after 1996, so early decades undercount.
When was the last recorded flood event in Williamson County?
19 Jul 2025 (Flash Flood). Records reach NCEI about 120 days after the month ends.
What was the most damaging flood event recorded in Williamson County?
The flash flood of 10 May 1996, with property damage estimated by NCEI at $1.0M.
How does Williamson County compare with Illinois for flood?
16.2 events per 100 square miles against 11.7 statewide; the county holds 68 of the state's 6,507 recorded events.
Provenance
NOAA NCEI Storm Events Database, yearly details files through 30 Jun 2026, public domain. County-recorded events plus zone-recorded events whose forecast zone is named for the county (marked "Forecast zone"). Population and area from the US Census Bureau (2021). Built 1 Oct 2026. See the methodology, the Flood hub and the county page.