1420

1420 (MCDXX) was a leap year starting on Monday of the Julian calendar, the 1420th year of the Common Era (CE) and Anno Domini (AD) designations, the 420th year of the 2nd millennium, the 20th year of the 15th century, and the 1st year of the 1420s decade. As of the start of 1420, the Gregorian calendar was 9 days ahead of the Julian calendar, which was the dominant calendar of the time.

• May 21 – Treaty of Troyes. With the Burgundian faction dominant in France, King Charles VI of France acknowledges Henry V of England as his heir and as virtual ruler of most of France.
• May 25 – Henry the Navigator is appointed governor of the Order of Christ.
• The Madeira Islands were discovered by the Portuguese João Gonçalves Zarco.
• Hussite Wars – Sigismund, Holy Roman Emperor fails at the battle of Vysehrad and is ejected from Bohemia.
• Catherine of Valois marries Henry V of England.
• Henry V of England starts the construction Grace Dieu (ship)
• Construction begins on the Temple of Heaven in Beijing, China while the Forbidden City is completed.
• World population reaches 3.75 million.

• November 24 – John Stafford, 1st Earl of Wiltshire, English politician (died 1473)
• date unknown
  • Jean Fouquet, French painter (died 1481)
  • Nicolas Jenson, French engraver (died 1480)

• June 11 – John III, Burgrave of Nuremberg (born c.1369)
• August 9 – Pierre d'Ailly, French theologian and cardinal (born 1351)
• September 3 – Robert Stewart, 1st Duke of Albany, regent of Scotland
• date unknown
  • Epiphanius the Wise, Russian saint
  • Andrew of Wyntoun, Scottish chronicler (born 1350)