Hamilton County, Iowa

What hazards hit Hamilton County most?

The most frequent records are hail reports: 149 since 1974. 44% of its hail reports since 1974 fell in May and June. 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 Hamilton County had?

NOAA records 56 tornadoes in Hamilton County from 1963 to 2024, the strongest rated F4, with 1 death and 13 injuries recorded in the county. That is 14th of 99 Iowa counties and 280th of 3,080 U.S. 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 56 tornadoes whose track touched Hamilton County since 1950 (NOAA's county records number 56, the same count); along their whole tracks they killed 1 person.

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 Hamilton County?

The most recent record with damage, injuries or deaths is the August 9, 2025 lightning ($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 Hamilton 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?

44% of its hail reports since 1974 fell in May and June. The two busiest months are in violet.

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

Federal disaster declarations for Hamilton County

FEMA's register lists 21 declarations that include Hamilton County: 19 major disasters, 2 emergencies and 0 fire management assistance declarations. Most were for severe storm (9) and flood (7).

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 Hamilton County had?

NOAA's Storm Events Database holds 72 flood or flash flood records for Hamilton County from 1996 to 2019, on 61 days, with 1 death. By flood insurance claims since 1978 (OpenFEMA, as of September 8, 2026), Hamilton County ranks 1944th of 2,942 U.S. counties.

The National Flood Insurance Program has paid $189,000 on 28 claims filed in Hamilton County; the most in one year was 13 in 2010. 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 Hamilton County

FEMA's National Risk Index rates Hamilton County Relatively Low overall, with an expected annual loss of $15.5 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 Hamilton County

1. Story County 1,320
2. Webster County 1,007
3. Boone County 806
4. Hardin County 693
5. Hamilton County 683
6. Franklin County 602
7. Wright County 598

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
• Hail in IowaThe state's hail reports, 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 Hamilton CountyThe hazard risk calculator: 18 hazards beside the county's record
• Download Hamilton County's FEMA declarations (CSV)21 rows: every declaration that named the county, for your own analysis