Williamson County, Illinois

What hazards hit Williamson County most?

The most frequent records are severe thunderstorm wind events: 142 since 1966. The rank column places the county among Illinois's counties by days with a record per 1,000 square miles of land over each hazard's complete period.

Source: NOAA NCEI Storm Events Database (county and forecast-zone records attributed to the county; a zone record shows its own totals on each county it covers). Days: dates with at least one record of the hazard in the county. Ranks: days with a record per 1,000 square miles of land (Census Bureau 2024 Gazetteer), since 1950 for tornadoes, 1955 for hail and thunderstorm wind, 1996 for the rest.

How many tornadoes has Williamson County had?

NOAA records 22 tornadoes in Williamson County from 1957 to 2025, the strongest rated EF4, with 10 deaths and 214 injuries recorded in the county. A tornado that crossed a county line is counted in each county it touched, with the length of its path inside the county.

Counted as whole tornadoes rather than county records, the Storm Prediction Center's database holds 23 tornadoes whose track touched Williamson County since 1950 (NOAA's county records number 22: they file a crossing tornado once per county segment, and the two databases differ on some tracks); along their whole tracks they killed 21 people, 10 of them in Williamson County.

Map of the strongest tornado tracks in Illinois.

Source: NOAA NCEI Storm Events Database, tornado records by county (path length in the county, maximum width); ratings as published: F scale before February 1, 2007, EF scale after. Whole-track figures: NOAA Storm Prediction Center tornado database (1950-2025). SPC severe weather database.

When was the last damaging storm in Williamson County?

The most recent record with damage, injuries or deaths is the April 27, 2026 thunderstorm wind ($35,000 in damage in 2025 dollars).

A surging portion of a storm line caused damage along Cedar Grove Rd north of Marion. Multiple trees were snapped or uprooted. Shingle damage occurred to homes and buildings. A play set was torn up and parts of fences downed.
National Weather Service event narrative, NOAA Storm Events Database (search the full record, event 1348301)

Source: NOAA NCEI Storm Events Database; every record of 2025-2026 is listed, earlier ones when they caused deaths, injuries or $250,000 of damage (2025 dollars), and every tornado.

The deadliest and costliest records

A damage figure marked "step" is a record from before 1993: NOAA then filed damage by category, and the figure is the category as entered, in the dollars of that year, not an estimate of the loss.

Source: NOAA NCEI Storm Events Database: deaths and injuries direct and indirect; damage is property plus crops as estimated by the National Weather Service, converted to 2025 dollars.

Is it getting more frequent?

Records per decade for Williamson County's most frequent hazards. Counts rose everywhere after 1996, when NOAA began recording every event type, so compare decades within a hazard's complete period only (the shaded cells come before it).

Fog, smoke and funnel clouds in the 2010s: 62 records against 19 in the decade before, 55 of them forecast-zone records. Heat in the 2010s: 39 records against 13 in the decade before, 39 of them forecast-zone records. Cells marked z rose mostly through zone records. The local National Weather Service office files these once per forecast zone, so a change in how it draws its zones or splits a storm into records moves this count as much as the weather does; read it beside the Williamson County days with a record above.

Source: NOAA NCEI Storm Events Database, records per calendar decade; zone records from the CZ_TYPE field (Z).

What time of year?

Records by month in Williamson County. The two busiest months are in violet.

Source: NOAA NCEI Storm Events Database, records by the month they began.

Federal disaster declarations for Williamson County

FEMA's register lists 9 declarations that include Williamson County: 6 major disasters, 3 emergencies and 0 fire management assistance declarations. Most were for severe storm (3) and biological (2).

Source: FEMA OpenFEMA Disaster Declarations Summaries (v2), declarations through October 2, 2026; one declaration is counted once however many areas it names. OpenFEMA dataset page.

How many floods has Williamson County had?

NOAA's Storm Events Database holds 68 flood or flash flood records for Williamson County from 1996 to 2025, on 61 days, with 1 death. By flood insurance claims since 1978 (OpenFEMA, as of September 8, 2026), Williamson County ranks 853rd of 2,942 U.S. counties.

The National Flood Insurance Program has paid $2.1 million on 239 claims filed in Williamson County; the most in one year was 38 in 1996. Claims count insured losses only: uninsured flood damage is not in this file.

Source: FEMA OpenFEMA NFIP Redacted Claims, as of September 8, 2026; claims by year of loss, payments in the dollars of the year paid. OpenFEMA dataset page.

FEMA's modeled risk for Williamson County

FEMA's National Risk Index rates Williamson County Relatively Moderate overall, with an expected annual loss of $52.5 million. These are FEMA's model estimates of future loss from 18 hazards, not a count of what happened; they can differ from the record above.

Source: FEMA National Risk Index, county table, December 2025 release. FEMA's National Risk Index map.

Counties that share a border with Williamson County

1. Jackson County 1,435
2. Franklin County 1,179
3. Saline County 1,044
4. Union County 1,025
5. Williamson County 892
6. Johnson County 719

Source: U.S. Census Bureau county adjacency file; NOAA NCEI Storm Events Database, records since 1950. The Census Bureau's adjacency file.

Next

• Tornadoes in IllinoisEvery Illinois tornado since 1950 and the counties with the most per square mile
• Severe thunderstorm wind in IllinoisThe state's severe thunderstorm wind events, by county, year and month
• The Illinois recordEvery hazard in the state, its deadliest events and its federal declarations
• FEMA's risk rating for each hazard in Williamson CountyThe hazard risk calculator: 18 hazards beside the county's record
• Download Williamson County's FEMA declarations (CSV)9 rows: every declaration that named the county, for your own analysis