- Apr 1 Samuel Morey is issued the first U.S. patent for an internal-combustion engine, which he calls a “Gas or Vapour Engine"
- Apr 10 The 10,500 inhabitants of the Greek town Messolonghi start leaving the town after a year's siege by Turkish forces. Very few of them survive.
- Apr 12 Weber's opera "Oberon" premieres in London
- Apr 23 Missolonghi, Greece captured by Turks