F0/EF0 1 2 3 4 5 · Lines run from where each tornado touched down to where it lifted; dots are short paths. Neighboring counties are outlined.
When tornadoes hit Grundy County
May has brought the most, 14 of 36. About 83% touched down between 1 pm and 7 pm (Central Standard Time, as the Storm Prediction Center records it).
By decade
More tornadoes in recent decades mostly reflects better detection and reporting (Doppler radar, storm spotters, damage surveys), especially for weak EF0 tornadoes, not necessarily more storms. The 2020s bar covers only 2020 to 2024.
How strong they were
| Rating | Estimated 3-second gust | Tornadoes |
|---|---|---|
| F0 / EF0 | Light damage: 65 to 85 mph (EF scale) | 11 |
| F1 / EF1 | Moderate: 86 to 110 mph | 16 |
| F2 / EF2 | Considerable: 111 to 135 mph | 6 |
| F3 / EF3 | Severe: 136 to 165 mph | 1 |
| F4 / EF4 | Devastating: 166 to 200 mph | 1 |
| F5 / EF5 | Incredible: over 200 mph | 1 |
Tornadoes before February 2007 were rated on the original Fujita (F) scale; since then the National Weather Service uses the Enhanced Fujita (EF) scale. Wind speeds above are EF-scale estimates from damage, not measurements. See what the EF scale means.
The strongest tornadoes in Grundy County
| Date | Rating | Path length | Path width | Deaths | Injuries |
|---|---|---|---|---|---|
| May 25, 2008 | EF5 | 41 mi | 2,100 yd | 9 | 70 |
| May 30, 1989 | F4 | 11 mi | 200 yd | 3 | |
| April 16, 1960 | F3 | 29.8 mi | 800 yd | 1 | 5 |
| April 19, 1966 | F2 | 2.3 mi | 200 yd | ||
| October 14, 1966 | F2 | 2.7 mi | 100 yd | ||
| March 22, 1991 | F2 | 20 mi | 50 yd | ||
| July 2, 1999 | F2 | 8.5 mi | 50 yd | ||
| May 10, 2001 | F2 | 1.7 mi | 200 yd | ||
| May 10, 2001 | F2 | 8 mi | 875 yd | ||
| May 31, 1971 | F1 | 2.3 mi | 200 yd |
Deaths and injuries are for each tornado’s whole path, which can cross other counties.
The deadliest
The deadliest tornado to touch Grundy County was an EF5 on May 25, 2008. It killed 9 people and injured 70 along its 41-mile path.
Most recent tornadoes
| Date | Rating | Path length | Path width | Deaths | Injuries |
|---|---|---|---|---|---|
| March 31, 2023 | EF1 | 4.1 mi | 80 yd | ||
| March 31, 2023 | EF1 | 3.5 mi | 80 yd | ||
| November 28, 2016 | EF0 | 1.5 mi | 25 yd | ||
| November 28, 2016 | EF0 | 5.7 mi | 50 yd | ||
| July 6, 2014 | EF0 | 1.5 mi | 20 yd | ||
| July 6, 2014 | EF1 | 3.2 mi | 100 yd | ||
| June 29, 2014 | EF1 | 1.9 mi | 50 yd | ||
| June 21, 2009 | EF1 | 2.1 mi | 70 yd |
The official database ends with 2024. For storms since then, see the Storm Prediction Center’s reports and your local National Weather Service office.
FEMA’s tornado risk rating
FEMA’s National Risk Index rates the tornado risk in Grundy County as relatively low, with a score of 35 out of 100 compared with every other U.S. county. It estimates about 0.52 tornadoes a year here and an expected annual loss of about $1,148,289 to buildings, people and farming. The index mixes how often tornadoes strike with what is exposed and how well a community can recover, so a busy rural county can rate lower than a less active city.
Neighboring counties
- Tama County, IA: 48 tornadoes
- Hardin County, IA: 44 tornadoes
- Marshall County, IA: 39 tornadoes
- Black Hawk County, IA: 38 tornadoes
- Butler County, IA: 29 tornadoes
Staying safe
When a tornado warning is issued, act at once. Go to a basement, storm shelter or safe room. With none, use a small windowless room on the lowest floor, as far from outside walls as you can, and cover your head and neck. Mobile homes and cars are not safe places to ride out a tornado: leave early for a sturdy building or shelter. Read the full tornado safety guide and the National Weather Service advice linked below.
Sources
- NOAA Storm Prediction Center: Severe Weather Database, tornadoes 1950 to 2024 (public domain)
- FEMA National Risk Index, tornado county data (December 2025 release)
- NOAA Storm Prediction Center: The Enhanced Fujita Scale (EF scale)
- National Weather Service: Tornado safety
Sources last checked 1 November 2026.