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Flood in Johnson County, Illinois
26 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.
Johnson County, Illinois, has 26 flood events in the NCEI record since 1950, with at least one in 17 different years.
May is the busiest month, with 6 of the recorded events. The last 20 years account for 10 events against 16 in the 20 years before, a change that reflects reporting practice as much as weather.
The county holds 0.4% of the 6,507 flood events recorded in Illinois; its 7.6 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 | Johnson County | Illinois | US |
|---|---|---|---|
| Flood events since 1950 | 26 | 6,507 | 183,559 |
| Per 100 square miles | 7.6 | 11.7 | 5.2 |
| Per 10,000 residents | 19.3 | 5.1 | 5.5 |
| Deaths recorded | 1 | 61 | 2,961 |
| Busiest month | May | June | June |
By year
Seasonality
2Feb
1Mar
3Apr
3May
6Jun
2Jul
2Aug
3Sep
0Oct
0Nov
1Dec
3
Recorded events
All 26 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 |
|---|---|---|---|---|---|---|---|
| 8 May 2024 | Flood | — | — | — | — | — | County |
| 17 Feb 2022 | Flash Flood | — | — | — | — | — | County |
| 12 Aug 2020 | Flood | — | — | — | — | — | County |
| 7 Jul 2016 | Flood | — | — | — | — | — | County |
| 7 Jul 2016 | Flood | — | $15K | — | 1 | 1 | County |
| 21 Dec 2013 | Flood | — | — | — | — | — | County |
| 1 May 2011 | Flood | — | $120K | — | — | — | County |
| 24 Apr 2011 | Flood | — | $10K | — | — | — | County |
| 3 Apr 2008 | Flash Flood | — | — | — | — | — | County |
| 18 Mar 2008 | Flood | — | $1.6M | — | — | 2 | County |
| 19 Aug 2006 | Flash Flood | — | — | — | — | — | County |
| 9 Mar 2006 | Flash Flood | — | — | — | — | — | County |
| 15 Nov 2005 | Flash Flood | — | — | — | — | — | County |
| 6 May 2003 | Flash Flood | — | — | — | — | — | County |
| 4 May 2003 | Flash Flood | — | — | — | — | — | County |
| 17 May 2002 | Flash Flood | — | — | — | — | — | County |
| 23 Jan 2002 | Flood | — | $5K | — | — | — | Forecast zone |
| 17 Dec 2001 | Flood | — | — | — | — | — | Forecast zone |
| 17 Dec 2001 | Flash Flood | — | $40K | — | — | — | County |
| 10 Aug 2001 | Flood | — | — | — | — | — | County |
| 3 Jan 2000 | Flash Flood | — | $10K | — | — | — | County |
| 2 Jun 1999 | Flood | — | — | — | — | — | County |
| 29 Jun 1998 | Flash Flood | — | — | — | — | — | County |
| 1 Mar 1997 | Flash Flood | — | $20K | — | — | — | County |
| 10 May 1996 | Flash Flood | — | — | — | — | — | County |
| 29 Apr 1996 | Flash Flood | — | $50K | — | — | — | County |
Questions and answers
How many flood events has Johnson County had?
26 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 Johnson County?
8 May 2024 (Flood). Records reach NCEI about 120 days after the month ends.
What was the most damaging flood event recorded in Johnson County?
The flood of 18 Mar 2008, with property damage estimated by NCEI at $1.6M.
How does Johnson County compare with Illinois for flood?
7.6 events per 100 square miles against 11.7 statewide; the county holds 26 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.