What is the largest tornado outbreak known in history (by number of tornadoes)?

The largest tornado outbreak known by number of tornadoes is the 2011 Super Outbreak. It swept across the southern, Midwestern, and northeastern United States from April 25 through April 28, 2011, producing 368 confirmed tornadoes.

April 27 was the outbreak’s extraordinary peak. That single day produced 224 confirmed tornadoes, including four rated EF5, the highest category on the Enhanced Fujita scale. The storms affected 21 states and Ontario, Canada, with destructive activity extending from Texas to New York.

The outbreak killed 324 people in tornadoes and caused more than $10 billion in damage in 2011 dollars. It is sometimes confused with the 1974 Super Outbreak, which produced fewer tornadoes but seven F5 tornadoes and remains notable for its exceptional intensity. “Largest” here refers to the number of confirmed tornadoes, not the number of deaths, strongest tornadoes, or overall damage.