Sioux County, Iowa

What hazards hit Sioux County most?

The most frequent records are hail reports: 261 since 1961. 49% of its hail reports since 1961 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 Sioux County had?

NOAA records 47 tornadoes in Sioux County from 1963 to 2024, the strongest rated F3, with 0 deaths and 0 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 50 tornadoes whose track touched Sioux County since 1950 (NOAA's county records number 47: 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 Sioux County?

The most recent record with damage, injuries or deaths is the December 18, 2025 blizzard (3 injuries).

Periods of light snowfall along with winds of 40 to 60 mph resulted in periods of whiteout conditions. Travel was not recommended during the early and mid-afternoon. A two-vehicle, three-injury accident occurred 1 mile west of Boyden when low visibility resulted in a rear-end collision, which pushed one of the vehicles into a bridge guardrail.
National Weather Service event narrative, NOAA Storm Events Database (search the full record, event 1307576)

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

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 Sioux 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: 39 records against 10 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 Sioux 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?

49% of its hail reports since 1961 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 Sioux County

FEMA's register lists 15 declarations that include Sioux County: 12 major disasters, 3 emergencies and 0 fire management assistance declarations. Most were for severe storm (6) and flood (5).

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 Sioux County had?

NOAA's Storm Events Database holds 164 flood or flash flood records for Sioux County from 1996 to 2026, on 100 days, with 1 death. By flood insurance claims since 1978 (OpenFEMA, as of September 8, 2026), Sioux County ranks 1731st of 2,942 U.S. counties.

The National Flood Insurance Program has paid $4.0 million on 43 claims filed in Sioux County; the most in one year was 25 in 2024. 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 Sioux County

FEMA's National Risk Index rates Sioux County Relatively Low overall, with an expected annual loss of $29.8 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 Sioux County

1. Sioux County 1,046
2. Plymouth County 1,017
3. Lincoln County, SD 959
4. Union County, SD 834
5. O'Brien County 826
6. Lyon County 774
7. Cherokee County 708
8. Osceola County 607

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