Lyon County, Iowa

What hazards hit Lyon County most?

The most frequent records are winter storm records: 195 since 1996. 48% of its winter storm records since 1996 fell in December and January. The rank column places the county among Iowa'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 Lyon County had?

NOAA records 43 tornadoes in Lyon County from 1951 to 2025, the strongest rated EF2, with 1 death and 2 injuries recorded in the county. That is 19th of 99 Iowa 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 45 tornadoes whose track touched Lyon County since 1950 (NOAA's county records number 43: they file a crossing tornado once per county segment, and the two databases differ on some tracks); along their whole tracks they killed 1 person.

Map of the strongest tornado tracks in Iowa.

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 Lyon County?

The most recent record with damage, injuries or deaths is the June 20, 2024 flood ($12.4 million in damage in 2025 dollars).

Rainfall amounts across Lyon County from June 20-22 ranged from 7 to 12 inches. Widespread overland flooding ensued with additional major to record flooding along the Big Sioux, Rock, and Little Rock Rivers, and Mud Creek. At the peak of flooding, approximately 50 people were evacuated from Rock Rapids, Doon, and Alvord. In Rock Rapids, there were 12 swift water rescues when flood waters overwhelmed the city. County-wide 605 homes were impacted by flood waters, 15 of which were declared a total loss. In addition, six businesses were declared a total loss. Reported damage to individual property is estimated to cost 2.7 million dollars. County infrastructure was also severely impacted. Nearly all gravel roads had some type of washout and 12 county bridges were impacted by flood waters. Preliminary damage assessments estimate damage to public infrastructure to be 10.5 million dollars. …
National Weather Service event narrative, NOAA Storm Events Database (search the full record, event 1195603)

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 Lyon 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?

48% of its winter storm records since 1996 fell in December and January. The two busiest months are in violet.

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

Federal disaster declarations for Lyon County

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

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 Lyon County had?

NOAA's Storm Events Database holds 101 flood or flash flood records for Lyon County from 1997 to 2024, on 69 days, with 0 deaths. By flood insurance claims since 1978 (OpenFEMA, as of September 8, 2026), Lyon County ranks 1449th of 2,942 U.S. counties.

The National Flood Insurance Program has paid $1.7 million on 75 claims filed in Lyon County; the most in one year was 38 in 2014. 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 Lyon County

FEMA's National Risk Index rates Lyon County Very Low overall, with an expected annual loss of $10.9 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 Lyon County

1. Minnehaha County, SD 1,554
2. Sioux County 1,046
3. Lincoln County, SD 959
4. O'Brien County 826
5. Nobles County, MN 812
6. Lyon County 774
7. Rock County, MN 701
8. Osceola County 607

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 IowaEvery Iowa tornado since 1950 and the counties with the most per square mile
• Winter storms in IowaThe state's winter storm records, by county, year and month
• The Iowa recordEvery hazard in the state, its deadliest events and its federal declarations
• FEMA's risk rating for each hazard in Lyon CountyThe hazard risk calculator: 18 hazards beside the county's record
• Download Lyon County's FEMA declarations (CSV)16 rows: every declaration that named the county, for your own analysis