Johnson County, Iowa

What hazards hit Johnson County most?

The most frequent records are severe thunderstorm wind events: 282 since 1958. 41% of its severe thunderstorm wind events since 1958 fell in June and July. 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 Johnson County had?

NOAA records 46 tornadoes in Johnson County from 1962 to 2026, the strongest rated F3, with 1 death and 51 injuries recorded in the county. That is 49th 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 Johnson County since 1950 (NOAA's county records number 46: they file a crossing tornado once per county segment, and the two databases differ on some tracks); along their whole tracks they killed 4 people, 1 of them in Johnson County.

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 Johnson County?

The most recent record with damage, injuries or deaths is the March 31, 2023 tornado (2 injuries).

A tornado developed just southwest of Coralville, crossed Highway 218 and damaged the James St. Warehouse near Highway 6 in Coralville. Several trailers and a truck were flipped over in the vicinity. A retail building also had part of a roof lifted off with several vehicles rolled or flipped. The tornado then tracked into a residential area and uprooted and snapped numerous trees. At least 2 injuries were reported by emergency management. Damage then became more sporadic before the tornado reintensified across Coralville Reservoir. A more concentrated path began near Sugar Bottom campground east of North Liberty and continued northeast towards Solon. A radio tower collapsed and a roof was lifted off a home and partially removed. The tornado continued northeast into a field before eventually reaching another farmstead and destroying an outbuilding. …
National Weather Service event narrative, NOAA Storm Events Database (search the full record, event 1087096)

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 Johnson 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?

41% of its severe thunderstorm wind events since 1958 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 Johnson County

FEMA's register lists 24 declarations that include Johnson County: 22 major disasters, 2 emergencies and 0 fire management assistance declarations. Most were for flood (12) and severe storm (7).

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 Johnson County had?

NOAA's Storm Events Database holds 75 flood or flash flood records for Johnson County from 1996 to 2026, on 58 days, with 0 deaths. By flood insurance claims since 1978 (OpenFEMA, as of September 8, 2026), Johnson County ranks 557th of 2,942 U.S. counties.

The National Flood Insurance Program has paid $31.9 million on 446 claims filed in Johnson County; the most in one year was 181 in 2008. 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 Johnson County

FEMA's National Risk Index rates Johnson County Relatively Moderate overall, with an expected annual loss of $96.3 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 Johnson County

1. Linn County 1,436
2. Benton County 989
3. Johnson County 901
4. Cedar County 737
5. Muscatine County 726
6. Iowa County 600
7. Washington County 583
8. Louisa County 457

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
• Severe thunderstorm wind in IowaThe state's severe thunderstorm wind events, 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 Johnson CountyThe hazard risk calculator: 18 hazards beside the county's record
• Download Johnson County's FEMA declarations (CSV)24 rows: every declaration that named the county, for your own analysis