Lyman County, South Dakota

What hazards hit Lyman County most?

The most frequent records are severe thunderstorm wind events: 301 since 1957. 66% of its severe thunderstorm wind events since 1957 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 Lyman County had?

NOAA records 40 tornadoes in Lyman County from 1960 to 2025, the strongest rated F3, with 0 deaths and 2 injuries 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 43 tornadoes whose track touched Lyman County since 1950 (NOAA's county records number 40: 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 Lyman County?

The most recent record with damage, injuries or deaths is the January 16, 2026 winter weather (2 deaths).

At 3:44 PM, the Lyman County Sheriff responded to a five-vehicle accident on Interstate 90, five miles west of Reliance. The collision occurred when a vehicle slowed due to near-blizzard conditions caused by high winds and snow showers. The South Dakota Department of Transportation mesonet station, located three miles west-northwest of Reliance, recorded wind gusts between 37 and 40 mph at the time of the incident. The chain-reaction accident resulted in eight injuries and two fatalities.
National Weather Service event narrative, NOAA Storm Events Database (search the full record, event 1300820)

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

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 Lyman 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?

66% of its severe thunderstorm wind events since 1957 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 Lyman County

FEMA's register lists 16 declarations that include Lyman County: 13 major disasters, 3 emergencies and 0 fire management assistance declarations. Most were for flood (7) and severe storm (4).

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 Lyman County had?

NOAA's Storm Events Database holds 38 flood or flash flood records for Lyman County from 1997 to 2025, on 35 days, with 2 deaths. By flood insurance claims since 1978 (OpenFEMA, as of September 8, 2026), Lyman County ranks 2181st of 2,942 U.S. counties.

The National Flood Insurance Program has paid $393,000 on 16 claims filed in Lyman County; the most in one year was 13 in 2019. 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 Lyman County

FEMA's National Risk Index rates Lyman County Very Low overall, with an expected annual loss of $5.9 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 Lyman County

1. Charles Mix County 958
2. Lyman County 927
3. Hughes County 801
4. Tripp County 795
5. Gregory County 751
6. Brule County 707
7. Stanley County 703
8. Hyde County 568
9. Jones County 540
10. Mellette County 488
11. Buffalo County 416

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 Lyman CountyThe hazard risk calculator: 18 hazards beside the county's record
• Download Lyman County's FEMA declarations (CSV)16 rows: every declaration that named the county, for your own analysis