Sioux County, Iowa: Natural Disaster Risk and History
Sioux County, Iowa has a Relatively Low natural-hazard risk rating in FEMA's National Risk Index (v1.20, December 2025): a score of 52.4 out of 100, higher than about 52% of US counties, with hail, winter storms and tornadoes scoring highest of its 18 hazards and $30 million a year in expected losses.
OpenFEMA lists 13 federal disaster declarations that included Sioux County since 1965, not counting 2 for COVID-19; the latest is DR-4796-IA (Severe Storms, Flooding, Straight-Line Winds, and Tornadoes, declared 24 June 2024). NOAA's Storm Prediction Center recorded 49 tornadoes touching Sioux County from 1950 to 2025.
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Population 35,872 Buildings worth $15 billion Area 777 sq mi Risk rank in Iowa 23 of 99 FIPS 19167
All 18 hazards, highest risk first
FEMA National Risk Index| Hazard | Risk rating | Score | Expected loss a year | How often | Events in record |
|---|---|---|---|---|---|
| Hail | Relatively High | 95.5 | $5.7 million | about 6.5 a year | 247 |
| Winter weather | Relatively High | 87.0 | $557,274 | about 17 a year | 320 |
| Tornado | Relatively Moderate | 79.4 | $6.6 million | about once every 1.5 years | 49 |
| Ice storm | Relatively Moderate | 71.8 | $420,588 | about once a year | 66 |
| Drought | Relatively Moderate | 71.5 | $1.0 million | about 24 a year | 805 |
| Cold wave | Relatively Low | 60.9 | $2.5 million | about 7.5 a year | 143 |
| Inland flooding | Relatively Low | 49.5 | $11 million | about 3.3 a year | 92 |
| Strong wind | Relatively Low | 49.1 | $934,477 | about 4.4 a year | 167 |
| Heat wave | Relatively Low | 40.7 | $412,276 | about 5.9 a year | 98 |
| Wildfire | Very Low | 39.7 | $44,287 | rarer than once in 1,000 years | — |
| Landslide | Very Low | 30.2 | $538 | about once every 12 years | — |
| Lightning | Relatively Low | 29.9 | $186,882 | about 39 a year | 90,913 strikes |
| Earthquake | Very Low | 19.1 | $45,517 | rarer than once in 1,000 years | — |
| Avalanche | Not Applicable | — | — | — | — |
| Coastal flooding | Not Applicable | — | — | — | — |
| Hurricane | Not Applicable | — | — | — | — |
| Tsunami | Not Applicable | — | — | — | — |
| Volcanic activity | Not Applicable | — | — | — | — |
Score: FEMA's percentile among US counties that face the hazard (higher = more risk). Expected loss: FEMA's modelled average yearly loss to buildings, people (as a statistical value) and crops. How often: FEMA's annualised frequency of the hazard in the county; for some hazards it counts event-days, so it is a rough guide, not a forecast. "Not Applicable" means FEMA does not model that hazard here.
Federal disaster declarations 13
Most common: Severe Storm 6, Flood 5, Hurricane 1, Drought 1.
| Decade | Declarations | Incident types |
|---|---|---|
| 1960s | 2 | Flood ×2 |
| 1970s | 1 | Drought |
| 1990s | 1 | Flood |
| 2000s | 1 | Hurricane |
| 2010s | 7 | Severe Storm ×5, Flood ×2 |
| 2020s | 1 | Severe Storm |
The last 10
Widest declarations that included Sioux County
- Hurricane Katrina Evacuation (2005, EM-3239-IA): 99 Iowa counties designated.
- Severe Storms & Flooding (1993, DR-996-IA): 99 Iowa counties designated.
- Severe Storms and Flooding (2019, DR-4421-IA): 80 Iowa counties designated.
Named storms in its declarations: Hurricane Katrina (2005).
Not counted above: 2 COVID-19 ("Biological") declarations — in 2020 every US county was included. Iowa also had 7 statewide declarations with no county list.
Tornado record since 1950 49
| Tornadoes touching the county | 49 |
|---|---|
| Strongest-rated | (E)F3 ×2 |
| Peak month | May (15) |
| Deadliest | 5 Apr 1958, F1, 37 mi path, 0 killed, 1 injured |
| Longest path | 5 Apr 1958, F1, 37 mi path, 0 killed, 1 injured |
| Most recent | 31 May 2024, EF0, 0.7 mi path |
| Deaths / injuries on those paths | 0 / 1 |
| Rating | (E)F0 | (E)F1 | (E)F2 | (E)F3 | (E)F4 | (E)F5 | Unrated |
|---|---|---|---|---|---|---|---|
| Count | 30 | 10 | 5 | 2 | 0 | 0 | 2 |
| Decade | 1950s | 1960s | 1970s | 1980s | 1990s | 2000s | 2010s | 2020s |
|---|---|---|---|---|---|---|---|---|
| Count | 1 | 5 | 4 | 1 | 8 | 11 | 13 | 6 |
Deaths and injuries are for each tornado's whole path, which can run beyond this county. F-scale ratings before February 2007, Enhanced Fujita (EF) after.
How Sioux County compares with its 5 nearest counties
| County | Distance | Overall risk | Score | Top hazard |
|---|---|---|---|---|
| Sioux County (this page) | — | Relatively Low | 52.4 | Hail |
| Lyon County | 33 km | Very Low | 19.2 | Hail |
| Plymouth County | 38 km | Relatively Low | 49.2 | Hail |
| O'Brien County | 45 km | Very Low | 16.4 | Hail |
| Union County, SD | 48 km | Very Low | 37.1 | Wildfire |
| Lincoln County, SD | 49 km | Relatively Low | 63.0 | Winter weather |
Nearest by distance between county centres. Every county in Iowa, ranked.
Vulnerability and resilience
| Social vulnerability | Very Low 10.6 |
|---|---|
| Community resilience | Very High 95.1 |
| Community risk factor | 0.60 |
| Expected annual loss, all hazards | $30 million |
FEMA scales expected losses up where social vulnerability is high (people who may find it harder to prepare, evacuate or recover) and down where community resilience is high. A factor above 1 raises the risk score. For social vulnerability a high rating is worse; for resilience a high rating is better.
Prepare for Sioux County's main hazards
- Right now: National Weather Service alerts for Iowa · all official warnings on Global Incident Tracker.
- Hail: Weather alerts for Iowa
- Winter weather: Power outages now · Carbon monoxide in winter
- Tornado: Is there a tornado warning now?
- Your property's flood zone: FEMA Flood Map Service Center ↗ — this page cannot tell you that.
- Official preparedness guidance: Ready.gov ↗ and your county emergency management office.
What this page shows, and what it misses
FEMA's National Risk Index rates a whole county against every other US county; it is a planning-level estimate for nationwide comparison, not a flood-zone map and not a substitute for a local risk assessment or the risk to one home. Declarations are presidential disaster, emergency and fire management declarations that named this county; state declarations and SBA or USDA designations are not included. Tornadoes are counted when the county is one of up to four listed on the track; 670 tornadoes that crossed a state line carry no county list in NOAA's file and are left out.
Federal Emergency Management Agency (FEMA), National Risk Index Dataset: National Risk Index Counties - v1.20.0 (December 2025). Retrieved from https://services.arcgis.com/XG15cJAlne2vxtgt/ArcGIS/rest/services/National_Risk_Index_Counties/FeatureServer/0/query on November 2, 2026, 1:20 PM EST. This product uses the Federal Emergency Management Agency’s National Risk Index dataset API or downloadable datasets but is not endorsed by FEMA. The Federal Government or FEMA cannot vouch for the data or analyses derived from these data after the data have been retrieved from the Agency's website(s).
Federal Emergency Management Agency (FEMA), OpenFEMA Dataset: Disaster Declarations Summaries - v2, retrieved from https://www.fema.gov/api/open/v2/DisasterDeclarationsSummaries on November 2, 2026, 1:21 PM EST. This product uses the Federal Emergency Management Agency's OpenFEMA API, but is not endorsed by FEMA. The Federal Government or FEMA cannot vouch for the data or analyses derived from these data after the data have been retrieved from the Agency's website(s).
Tornado records: NOAA/NWS Storm Prediction Center, Severe Weather Database, tornadoes 1950–2025 (https://www.spc.noaa.gov/wcm/data/1950-2025_actual_tornadoes.csv, downloaded 2 November 2026). Public domain; not endorsed by NOAA. Compiled by Global Incident Tracker.
Questions about Sioux County
What natural disasters is Sioux County, Iowa most at risk from?
Sioux County, Iowa has a Relatively Low natural-hazard risk rating in FEMA's National Risk Index (v1.20, December 2025): a score of 52.4 out of 100, higher than about 52% of US counties, with hail, winter storms and tornadoes scoring highest of its 18 hazards and $30 million a year in expected losses.
How many federal disaster declarations has Sioux County had?
OpenFEMA lists 13 federal disaster declarations that included Sioux County since 1965, not counting 2 for COVID-19; the latest is DR-4796-IA (Severe Storms, Flooding, Straight-Line Winds, and Tornadoes, declared 24 June 2024). Another 7 Iowa declarations were made statewide without a county list.
How many tornadoes have hit Sioux County?
NOAA's Storm Prediction Center recorded 49 tornadoes touching Sioux County from 1950 to 2025. The deadliest: 5 Apr 1958, F1, 37 mi path, 0 killed, 1 injured (deaths and injuries are for the whole path).
Is the National Risk Index a flood zone map?
No. The National Risk Index is a planning-level estimate for a whole county, built for nationwide comparison. It does not tell you the flood zone or the risk of a single property: for that, look up the address on FEMA's Flood Map Service Center (msc.fema.gov) and ask your local floodplain manager.