April 30 is the 120th day of the year (121st in leap years) in the Gregorian calendar; 245 days remain until the end of the year.
311 – The Diocletianic Persecution of Christians in the Roman Empire ends.
1315 – Enguerrand de Marigny is hanged at the instigation of Charles, Count of Valois.
1513 – Edmund de la Pole, Yorkist pretender to the English throne, is executed on the orders of Henry VIII.
1598 – Juan de Oñate begins the conquest of Santa Fe de Nuevo México.
1598 – Henry IV of France issues the Edict of Nantes, allowing freedom of religion to the Huguenots.
1789 – On the balcony of Federal Hall on Wall Street in New York City, George Washington takes the oath of office to become the first President of the United States.
1803 – Louisiana Purchase: The United States purchases the Louisiana Territory from France for $15 million, more than doubling the size of the young nation.
1838 – Nicaragua declares independence from the Central American Federation.
1863 – A 65-man French Foreign Legion infantry patrol fights a force of nearly 2,000 Mexican soldiers to nearly the last man in Hacienda Camarón, Mexico.
1871 – The Camp Grant massacre takes place in Arizona Territory.
1885 – Governor of New York David B. Hill signs legislation creating the Niagara Reservation, New York's first state park, ensuring that Niagara Falls will not be devoted solely to industrial and commercial use.
1897 – J. J. Thomson of the Cavendish Laboratory announces his discovery of the electron as a subatomic particle, over 1,800 times smaller than a proton (in the atomic nucleus), at a lecture at the Royal Institution in London.[3] 1900 – Hawaii becomes a territory of the United States, with Sanford B. Dole as governor.
1905 – Albert Einstein completes his doctoral thesis at the University of Zurich.
1925 – Automaker Dodge Brothers, Inc is sold to Dillon, Read & Co. for US$146 million plus $50 million for charity.
1927 – The Federal Industrial Institute for Women opens in Alderson, West Virginia, as the first women's federal prison in the United States.
1937 – The Commonwealth of the Philippines holds a plebiscite for Filipino women on whether they should be extended the right to suffrage; over 90% would vote yes.