Plymouth County, Iowa

What hazards hit Plymouth County most?

The most frequent records are hail reports: 282 since 1955. 44% of its hail reports since 1955 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 Plymouth County had?

NOAA records 54 tornadoes in Plymouth County from 1951 to 2026, the strongest rated F3, with 0 deaths and 5 injuries recorded in the county. That is 35th 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 52 tornadoes whose track touched Plymouth County since 1950 (NOAA's county records number 54: 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 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 Plymouth County?

The most recent record with damage, injuries or deaths is the June 21, 2024 flood ($1.5 million in damage in 2025 dollars).

Rainfall amounts across Plymouth County from June 20-22 ranged from only a few hundredths across southern areas to around 2 inches across northern areas. Farther north and upstream, 6 to 10 inches of rain fell across portions of southeast South Dakota and northwest Iowa, with locally higher amounts near 12 inches. This rainfall resulted in major to record flooding along the Big Sioux and Floyd Rivers and extensive overland flooding along the adjoining flood plain. During peak flooding, areas between the Big Sioux River and Iowa Highway 12 were evacuated. The Willow Creek Campground in Le Mars was also evacuated. There were at least two water rescues, including 14 individuals. County-wide, 47 individual households reported flood damage at an estimated cost of 275 thousand dollars. …
National Weather Service event narrative, NOAA Storm Events Database (search the full record, event 1195684)

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 Plymouth 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).

Drought in the 2020-26: 46 records against 10 in the decade before, 46 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 Plymouth 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?

44% of its hail reports since 1955 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 Plymouth County

FEMA's register lists 16 declarations that include Plymouth County: 12 major disasters, 4 emergencies and 0 fire management assistance declarations. Most were for flood (6) and severe storm (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 Plymouth County had?

NOAA's Storm Events Database holds 139 flood or flash flood records for Plymouth County from 1996 to 2026, on 100 days, with 0 deaths. By flood insurance claims since 1978 (OpenFEMA, as of September 8, 2026), Plymouth County ranks 2003rd of 2,942 U.S. counties.

The National Flood Insurance Program has paid $606,000 on 25 claims filed in Plymouth County; the most in one year was 9 in 2014. 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 Plymouth County

FEMA's National Risk Index rates Plymouth County Relatively Low overall, with an expected annual loss of $17.6 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 Plymouth County

1. Woodbury County 1,213
2. Sioux County 1,046
3. Plymouth County 1,017
4. Union County, SD 834
5. O'Brien County 826
6. Cherokee County 708

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 Plymouth CountyThe hazard risk calculator: 18 hazards beside the county's record
• Download Plymouth County's FEMA declarations (CSV)16 rows: every declaration that named the county, for your own analysis