April 20 is the 110th day of the year in the Gregorian calendar (111th in leap years). There are 255 days remaining.

  1. 1534 - Jacques Cartier begins his voyage, in which he will discover Canada and Labrador.
  2. 1657 - Freedom of religion is granted to the Jews of New Amsterdam (later New York City).
  3. 1792 - France declares war on Austria, the beginning of French Revolutionary Wars.
  4. 1861 - American Civil War: Robert E. Lee resigns his commission in the United States Army in order to command the forces of the state of Virginia.
  5. 1871 - Civil Rights Act of 1871
  6. 1912 - Opening day for baseball stadiums Tiger Stadium in Detroit, Michigan, and Fenway Park in Boston, Massachusetts.
  7. 1914 - Seventeen men, women, and children die in the Ludlow Massacre during a bitter Colorado coal-miner's strike.
  8. 1918 - Manfred von Richthofen, aka The Red Baron, shoots down his 79th and 80th victims marking his final victories before his death the following day.
  9. 1926 - Western Electric and Warner Bros. announce Vitaphone, a process to add sound to film.
  10. 1939 - Boston Red Sox Hall-of-Fame outfielder, Ted Williams, makes his Major League debut at Fenway Park; Boston, Massachusetts.
  11. 1999: Staff and students evacuate Columbine High School shortly after the shooting.1953 - Project BLUEBIRD turns into Project MKULTRA.
  12. 1961 - Failure of the Bay of Pigs Invasion of US troops against Cuba.
  13. 1968 - A South African Airways Boeing 707 crashes during takeoff at Windhoek, South-West Africa, killing 122.
  14. 1972 - Apollo 16 lands on the Moon.
  15. 1998 - TAME Boeing 727-200 chartered by Air France crashes into Cerro El Cable mountain after takeoff from Bogotá, Colombia, killing 53.
  16. 1999 - Eric Harris and Dylan Klebold kill 12 students and a teacher before killing themselves in the Columbine High School massacre.
  17. 1999 - Largest bombing of Kosovo by the United States in the Kosovo War.