Mercer County, Illinois

What hazards hit Mercer County most?

The most frequent records are severe thunderstorm wind events: 136 since 1957. 46% of its severe thunderstorm wind events since 1957 fell in June and July. 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 Mercer County had?

NOAA records 45 tornadoes in Mercer County from 1952 to 2026, the strongest rated F3, with 0 deaths and 3 injuries recorded in the county. That is 40th of 102 Illinois counties by days with tornadoes per 1,000 square miles since 1950. 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 46 tornadoes whose track touched Mercer County since 1950 (NOAA's county records number 45: they file a crossing tornado once per county segment, and the two databases differ on some tracks); along their whole tracks they killed 0 people.

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 Mercer County?

The most recent record with damage, injuries or deaths is the May 17, 2017 tornado ($30,000 in damage in 2025 dollars).

Tornado was rated a higher end EF-1 with peak winds 105 mph, a path length of 5.73 miles with a max path width of 150 yards. This higher end EF-1 tornado caused damage to numerous farm outbuildings, a few homes and trees across Mercer and Henry counties. One house partially lost a roof while another was impelled by flying debris. Approximately 30 to 40 trees were snapped at the trunks, a couple of dozen were uprooted, with about 50 trees experiencing limb damage. This tornado continued into Henry county.
National Weather Service event narrative, NOAA Storm Events Database (search the full record, event 703347)

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 Mercer 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).

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

What time of year?

46% of its severe thunderstorm wind events since 1957 fell in June and July. The two busiest months are in violet.

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

Federal disaster declarations for Mercer County

FEMA's register lists 15 declarations that include Mercer County: 11 major disasters, 4 emergencies and 0 fire management assistance declarations. Most were for flood (7) and snowstorm (3).

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 Mercer County had?

NOAA's Storm Events Database holds 55 flood or flash flood records for Mercer County from 1997 to 2025, on 48 days, with 0 deaths. By flood insurance claims since 1978 (OpenFEMA, as of September 8, 2026), Mercer County ranks 1558th of 2,942 U.S. counties.

The National Flood Insurance Program has paid $1.4 million on 61 claims filed in Mercer County; the most in one year was 32 in 1993. 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 Mercer County

FEMA's National Risk Index rates Mercer County Very Low overall, with an expected annual loss of $6.9 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 Mercer County

1. Henry County 905
2. Rock Island County 872
3. Des Moines County, IA 709
4. Mercer County 538
5. Knox County 521
6. Warren County 487
7. Louisa County, IA 457
8. Henderson County 410

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 Mercer CountyThe hazard risk calculator: 18 hazards beside the county's record
• Download Mercer County's FEMA declarations (CSV)15 rows: every declaration that named the county, for your own analysis