Walworth County, South Dakota

What hazards hit Walworth County most?

The most frequent records are severe thunderstorm wind events: 190 since 1960. 61% of its severe thunderstorm wind events since 1960 fell in June and July. 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 Walworth County had?

NOAA records 28 tornadoes in Walworth County from 1955 to 2025, the strongest rated F3, with 0 deaths and 2 injuries recorded in the county. That is 22nd of 66 South Dakota counties by days with tornadoes per 1,000 square miles since 1950. 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 30 tornadoes whose track touched Walworth County since 1950 (NOAA's county records number 28: 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 Walworth County?

The most recent record with damage, injuries or deaths is the June 1, 2019 flood ($3.7 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 863674)

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 Walworth 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).

Extreme cold in the 2010s: 20 records against 5 in the decade before, 20 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 Walworth 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?

61% of its severe thunderstorm wind events since 1960 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 Walworth County

FEMA's register lists 12 declarations that include Walworth County: 9 major disasters, 3 emergencies and 0 fire management assistance declarations. Most were for flood (5) and biological (2).

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.

FEMA's modeled risk for Walworth County

FEMA's National Risk Index rates Walworth County Very Low overall, with an expected annual loss of $10.2 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 Walworth County

1. Corson County 939
2. Edmunds County 819
3. Dewey County 814
4. Walworth County 663
5. McPherson County 650
6. Potter County 559
7. Campbell County 519

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
• Severe thunderstorm wind in South DakotaThe state's severe thunderstorm wind events, 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 Walworth CountyThe hazard risk calculator: 18 hazards beside the county's record
• Download Walworth County's FEMA declarations (CSV)12 rows: every declaration that named the county, for your own analysis