Union County, South Dakota: Natural Disaster Risk and History
Union County, South Dakota has a Very Low natural-hazard risk rating in FEMA's National Risk Index (v1.20, December 2025): a score of 37.1 out of 100, higher than about 37% of US counties, with wildfires, winter storms and drought scoring highest of its 18 hazards and $16 million a year in expected losses.
OpenFEMA lists 17 federal disaster declarations that included Union County since 1969, not counting 2 for COVID-19; the latest is DR-4807-SD (Severe Storms, Straight-Line Winds, and Flooding, declared 15 August 2024). NOAA's Storm Prediction Center recorded 21 tornadoes touching Union County from 1950 to 2025.
Live weather alerts for South Dakota All official warnings Latest FEMA declarations
Population 16,799 Buildings worth $6.0 billion Area 472 sq mi Risk rank in South Dakota 21 of 66 FIPS 46127
All 18 hazards, highest risk first
FEMA National Risk Index| Hazard | Risk rating | Score | Expected loss a year | How often | Events in record |
|---|---|---|---|---|---|
| Wildfire | Relatively Low | 77.6 | $447,485 | rarer than once in 1,000 years | — |
| Winter weather | Relatively Moderate | 77.5 | $256,468 | about 15 a year | 293 |
| Drought | Relatively Moderate | 74.6 | $951,217 | about 27 a year | 868 |
| Hail | Relatively Moderate | 73.5 | $916,983 | about 6.5 a year | 245 |
| Tornado | Relatively Moderate | 69.2 | $3.4 million | about once every 2.5 years | 16 |
| Ice storm | Relatively Moderate | 67.7 | $272,378 | about once a year | 67 |
| Inland flooding | Relatively Low | 47.5 | $8.5 million | about 3.6 a year | 101 |
| Landslide | Very Low | 35.8 | $670 | about once every 13 years | — |
| Cold wave | Relatively Low | 34.8 | $733,972 | about 6.5 a year | 123 |
| Heat wave | Very Low | 33.8 | $234,205 | about 6.5 a year | 106 |
| Lightning | Relatively Low | 32.1 | $164,218 | about 4 a year | 53,661 strikes |
| Strong wind | Relatively Low | 26.0 | $345,966 | about 4.1 a year | 156 |
| Earthquake | Very Low | 16.6 | $27,947 | 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 17
Most common: Flood 9, Severe Storm 6, Coastal Storm 1, Drought 1.
| Decade | Declarations | Incident types |
|---|---|---|
| 1960s | 1 | Flood |
| 1970s | 1 | Drought |
| 1980s | 1 | Flood |
| 1990s | 3 | Severe Storm ×2, Flood |
| 2000s | 1 | Coastal Storm |
| 2010s | 9 | Flood ×5, Severe Storm ×4 |
| 2020s | 1 | Flood |
The last 10
Widest declarations that included Union County
- Hurricane Katrina Evacuation (2005, EM-3234-SD): 66 South Dakota counties designated.
- Severe Flooding, Sever Winter Storms,heavy Rains High Winds (1997, DR-1173-SD): 66 South Dakota counties designated.
- Severe Winter Storms and Blizzard Conditions (1997, DR-1156-SD): 66 South Dakota 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. South Dakota also had 18 statewide declarations with no county list.
Tornado record since 1950 21
| Tornadoes touching the county | 21 |
|---|---|
| Strongest-rated | (E)F3 ×1 |
| Peak month | July (8) |
| Deadliest | 4 Jul 1994, F0, 1 mi path, 0 killed, 1 injured |
| Longest path | 12 Aug 1985, F1, 20 mi path |
| Most recent | 11 May 2014, EF0, 2.4 mi path |
| Deaths / injuries on those paths | 0 / 1 |
| Rating | (E)F0 | (E)F1 | (E)F2 | (E)F3 | (E)F4 | (E)F5 | Unrated |
|---|---|---|---|---|---|---|---|
| Count | 15 | 5 | 0 | 1 | 0 | 0 | 0 |
| Decade | 1950s | 1960s | 1970s | 1980s | 1990s | 2000s | 2010s | 2020s |
|---|---|---|---|---|---|---|---|---|
| Count | 1 | 4 | 1 | 6 | 3 | 5 | 1 | 0 |
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 Union County compares with its 5 nearest counties
| County | Distance | Overall risk | Score | Top hazard |
|---|---|---|---|---|
| Union County (this page) | — | Very Low | 37.1 | Wildfire |
| Clay County | 28 km | Very Low | 20.5 | Drought |
| Plymouth County, IA | 38 km | Relatively Low | 49.2 | Hail |
| Dixon County, NE | 42 km | Very Low | 8.8 | Hail |
| Sioux County, IA | 48 km | Relatively Low | 52.4 | Hail |
| Dakota County, NE | 50 km | Very Low | 36.0 | Hail |
Nearest by distance between county centres. Every county in South Dakota, ranked.
Vulnerability and resilience
| Social vulnerability | Very Low 10.6 |
|---|---|
| Community resilience | Relatively Moderate 48.3 |
| Community risk factor | 0.75 |
| Expected annual loss, all hazards | $16 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 Union County's main hazards
- Right now: National Weather Service alerts for South Dakota · all official warnings on Global Incident Tracker.
- Wildfire: US wildfires now · Wildfire smoke: what protects you
- Winter weather: Power outages now · Carbon monoxide in winter
- Drought: Drought monitor for South Dakota
- 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 Union County
What natural disasters is Union County, South Dakota most at risk from?
Union County, South Dakota has a Very Low natural-hazard risk rating in FEMA's National Risk Index (v1.20, December 2025): a score of 37.1 out of 100, higher than about 37% of US counties, with wildfires, winter storms and drought scoring highest of its 18 hazards and $16 million a year in expected losses.
How many federal disaster declarations has Union County had?
OpenFEMA lists 17 federal disaster declarations that included Union County since 1969, not counting 2 for COVID-19; the latest is DR-4807-SD (Severe Storms, Straight-Line Winds, and Flooding, declared 15 August 2024). Another 18 South Dakota declarations were made statewide without a county list.
How many tornadoes have hit Union County?
NOAA's Storm Prediction Center recorded 21 tornadoes touching Union County from 1950 to 2025. The deadliest: 4 Jul 1994, F0, 1 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.