Dewey County, South Dakota: Natural Disaster Risk and History
Dewey County, South Dakota has a Relatively Low natural-hazard risk rating in FEMA's National Risk Index (v1.20, December 2025): a score of 78.7 out of 100, higher than about 78% of US counties, with cold waves, winter storms and wildfires scoring highest of its 18 hazards and $22 million a year in expected losses.
OpenFEMA lists 14 federal disaster declarations that included Dewey County since 1976, not counting 2 for COVID-19; the latest is DR-4440-SD (Severe Winter Storm, Snowstorm, and Flooding, declared 7 June 2019). NOAA's Storm Prediction Center recorded 28 tornadoes touching Dewey County from 1950 to 2025.
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Population 5,228 Buildings worth $1.5 billion Area 2,470 sq mi Risk rank in South Dakota 2 of 66 FIPS 46041
All 18 hazards, highest risk first
FEMA National Risk Index| Hazard | Risk rating | Score | Expected loss a year | How often | Events in record |
|---|---|---|---|---|---|
| Cold wave | Very High | 99.0 | $20 million | about 9.2 a year | 175 |
| Winter weather | Relatively High | 85.3 | $159,170 | about 17 a year | 315 |
| Wildfire | Relatively Low | 83.0 | $317,633 | about once every 855 years | — |
| Ice storm | Relatively Moderate | 65.2 | $94,378 | about once every 1.8 years | 37 |
| Hail | Relatively Low | 57.8 | $195,475 | about 2.9 a year | 115 |
| Landslide | Very Low | 31.9 | $201 | about once a year | — |
| Drought | Very Low | 28.1 | $10,648 | about 5 a year | 1,267 |
| Tornado | Very Low | 24.4 | $192,176 | about once every 1.9 years | 21 |
| Heat wave | Very Low | 23.3 | $46,816 | about 2.8 a year | 41 |
| Strong wind | Relatively Low | 23.0 | $119,107 | about 2.3 a year | 89 |
| Inland flooding | Very Low | 17.4 | $1.2 million | about once a year | 27 |
| Lightning | Very Low | 16.4 | $31,392 | about 33 a year | 17,706 strikes |
| Earthquake | Very Low | 12.2 | $6,874 | 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 14
Most common: Severe Storm 7, Flood 3, Snowstorm 2, Coastal Storm 1.
| Decade | Declarations | Incident types |
|---|---|---|
| 1970s | 1 | Drought |
| 1990s | 3 | Flood, Severe Storm, Snowstorm |
| 2000s | 4 | Severe Storm ×2, Snowstorm, Coastal Storm |
| 2010s | 6 | Severe Storm ×4, Flood ×2 |
The last 10
Widest declarations that included Dewey 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 28
| Tornadoes touching the county | 28 |
|---|---|
| Strongest-rated | (E)F2 ×4 |
| Peak month | June (13) |
| Deadliest | 8 Jun 1964, F2, 3.8 mi path, 0 killed, 1 injured |
| Longest path | 2 Jun 1953, F2, 5.9 mi path |
| Most recent | 21 Jun 2014, EF0, 0.3 mi path |
| Deaths / injuries on those paths | 0 / 1 |
| Rating | (E)F0 | (E)F1 | (E)F2 | (E)F3 | (E)F4 | (E)F5 | Unrated |
|---|---|---|---|---|---|---|---|
| Count | 22 | 2 | 4 | 0 | 0 | 0 | 0 |
| Decade | 1950s | 1960s | 1970s | 1980s | 1990s | 2000s | 2010s | 2020s |
|---|---|---|---|---|---|---|---|---|
| Count | 2 | 5 | 2 | 2 | 7 | 8 | 2 | 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 Dewey County compares with its 5 nearest counties
| County | Distance | Overall risk | Score | Top hazard |
|---|---|---|---|---|
| Dewey County (this page) | — | Relatively Low | 78.7 | Cold wave |
| Ziebach County | 64 km | Very Low | 25.2 | Cold wave |
| Corson County | 65 km | Very Low | 38.1 | Cold wave |
| Walworth County | 74 km | Very Low | 39.5 | Cold wave |
| Potter County | 75 km | Very Low | 10.0 | Cold wave |
| Sully County | 79 km | Very Low | 6.3 | Wildfire |
Nearest by distance between county centres. Every county in South Dakota, ranked.
Vulnerability and resilience
| Social vulnerability | Very High 98.7 |
|---|---|
| Community resilience | Very Low 6.9 |
| Community risk factor | 1.87 |
| Expected annual loss, all hazards | $22 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 Dewey County's main hazards
- Right now: National Weather Service alerts for South Dakota · all official warnings on Global Incident Tracker.
- Cold wave: Carbon monoxide in winter · Power outages now
- Winter weather: Power outages now · Carbon monoxide in winter
- Wildfire: US wildfires now · Wildfire smoke: what protects you
- 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 Dewey County
What natural disasters is Dewey County, South Dakota most at risk from?
Dewey County, South Dakota has a Relatively Low natural-hazard risk rating in FEMA's National Risk Index (v1.20, December 2025): a score of 78.7 out of 100, higher than about 78% of US counties, with cold waves, winter storms and wildfires scoring highest of its 18 hazards and $22 million a year in expected losses.
How many federal disaster declarations has Dewey County had?
OpenFEMA lists 14 federal disaster declarations that included Dewey County since 1976, not counting 2 for COVID-19; the latest is DR-4440-SD (Severe Winter Storm, Snowstorm, and Flooding, declared 7 June 2019). Another 18 South Dakota declarations were made statewide without a county list.
How many tornadoes have hit Dewey County?
NOAA's Storm Prediction Center recorded 28 tornadoes touching Dewey County from 1950 to 2025. The deadliest: 8 Jun 1964, F2, 3.8 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.