Grundy County, Iowa

What hazards hit Grundy County most?

The most frequent records are severe thunderstorm wind events: 120 since 1960. 57% of its severe thunderstorm wind events since 1960 fell in June and July. The rank column places the county among Iowa'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 Grundy County had?

NOAA records 41 tornadoes in Grundy County from 1952 to 2025, the strongest rated F4, with 1 death and 2 injuries recorded in the county. That is 37th of 99 Iowa 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 40 tornadoes whose track touched Grundy County since 1950 (NOAA's county records number 41: they file a crossing tornado once per county segment, and the two databases differ on some tracks); along their whole tracks they killed 10 people, 1 of them in Grundy County.

Map of the strongest tornado tracks in Iowa.

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 Grundy County?

The most recent record with damage, injuries or deaths is the June 20, 2025 thunderstorm wind ($1,000 in damage in 2025 dollars).

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 Grundy 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?

57% of its severe thunderstorm wind events since 1960 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 Grundy County

FEMA's register lists 15 declarations that include Grundy County: 13 major disasters, 2 emergencies and 0 fire management assistance declarations. Most were for severe storm (8) and flood (4).

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 Grundy County had?

NOAA's Storm Events Database holds 56 flood or flash flood records for Grundy County from 1996 to 2024, on 46 days, with 0 deaths. By flood insurance claims since 1978 (OpenFEMA, as of September 8, 2026), Grundy County ranks 2262nd of 2,942 U.S. counties.

The National Flood Insurance Program has paid $31,000 on 13 claims filed in Grundy County; the most in one year was 5 in 2013. 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 Grundy County

FEMA's National Risk Index rates Grundy County Very Low overall, with an expected annual loss of $9.5 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 Grundy County

1. Black Hawk County 1,062
2. Marshall County 748
3. Butler County 734
4. Hardin County 693
5. Tama County 625
6. Franklin County 602
7. Grundy County 558

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 IowaEvery Iowa tornado since 1950 and the counties with the most per square mile
• Severe thunderstorm wind in IowaThe state's severe thunderstorm wind events, by county, year and month
• The Iowa recordEvery hazard in the state, its deadliest events and its federal declarations
• FEMA's risk rating for each hazard in Grundy CountyThe hazard risk calculator: 18 hazards beside the county's record
• Download Grundy County's FEMA declarations (CSV)15 rows: every declaration that named the county, for your own analysis