April 21
- 1887 – A long-track F4 tornado or tornado family killed at least 21 people as it moved across eastern Kansas and western Missouri. At least 12 died in Prescott, Kansas, where two-thirds of the buildings were damaged or destroyed, and 5 died near Sprague, Missouri. Another tornado killed 3 people near Schell City, Missouri.
- 1967 – The 1967 Oak Lawn tornado outbreak resulted in 58 deaths across Illinois. The worst casualties were from an F4 tornado that tore through the south side of Chicago and nearby suburbs, killing 33 people and injuring 1,000. Sixteen people died in Oak Lawn, Illinois when cars, stuck in rush hour traffic, were thrown from a highway. Another F4 tornado devastated Belvidere, killing 24 people and injuring 500. Of those, 13 deaths and 300 injuries were in school buses.