Sully County, South Dakota

What hazards hit Sully County most?

The most frequent records are hail reports: 146 since 1967. 59% of its hail reports since 1967 fell in July and August. The rank column places the county among South Dakota'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 Sully County had?

NOAA records 21 tornadoes in Sully County from 1965 to 2021, the strongest rated F2, with 0 deaths and 1 injury 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 22 tornadoes whose track touched Sully County since 1950 (NOAA's county records number 21: 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 South Dakota.

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 Sully County?

The most recent record with damage, injuries or deaths is the June 1, 2019 flood ($8.5 million in damage in 2025 dollars).

Spring snowmelt and heavy rain flooding from March, April, and May continued into June. This combined with above normal June rainfall resulted in hundreds of thousands of acres of crops damaged or unplanted across central and northeast South Dakota. For the entire state of South Dakota, nearly 4 million acres of crops were left unplanted as a result of the flooding. Total damaged or unplanted crop loss estimates for central and northeast South Dakota were near 307 million dollars.
National Weather Service event narrative, NOAA Storm Events Database (search the full record, event 863670)

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 Sully 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).

Source: NOAA NCEI Storm Events Database, records per calendar decade; zone records from the CZ_TYPE field (Z).

What time of year?

59% of its hail reports since 1967 fell in July and August. The two busiest months are in violet.

Source: NOAA NCEI Storm Events Database, records by the month they began.

Federal disaster declarations for Sully County

FEMA's register lists 16 declarations that include Sully County: 13 major disasters, 3 emergencies and 0 fire management assistance declarations. Most were for flood (6) and severe storm (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 Sully County had?

NOAA's Storm Events Database holds 14 flood or flash flood records for Sully County from 1997 to 2019, on 14 days, with 0 deaths. By flood insurance claims since 1978 (OpenFEMA, as of September 8, 2026), Sully County ranks 2590th of 2,942 U.S. counties.

The National Flood Insurance Program has paid $23,000 on 5 claims filed in Sully County; the most in one year was 4 in 1997. 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 Sully County

FEMA's National Risk Index rates Sully County Very Low overall, with an expected annual loss of $5.2 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 Sully County

1. Dewey County 814
2. Hughes County 801
3. Stanley County 703
4. Hyde County 568
5. Potter County 559
6. Sully County 525

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 South DakotaEvery South Dakota tornado since 1950 and the counties with the most per square mile
• Hail in South DakotaThe state's hail reports, by county, year and month
• The South Dakota recordEvery hazard in the state, its deadliest events and its federal declarations
• FEMA's risk rating for each hazard in Sully CountyThe hazard risk calculator: 18 hazards beside the county's record
• Download Sully County's FEMA declarations (CSV)16 rows: every declaration that named the county, for your own analysis