- Apr 7 Battle of Charleston, South Carolina failed Federal fleet attack on Fort Sumter
- Apr 10 Confederate General Earl Van Dorn attacks at Franklin, Tennessee
- Apr 11 Battle of Suffolk, Virginia (Norfleet House)
- Apr 12 -14] Gunboat battle at Bayou Teche, Louisiana
- Apr 13 Battle of Irish Bend, Louisiana (Fort Bisland)
- Apr 13 Society for the Relief of the Ruptured and Crippled is incorporated in the State of New York
- Apr 14 William Bullock patents continuous-roll printing press
- Apr 17 Grierson's raid begins as Colonel Grierson and 1700 horse troopers set off from La Grange, Tennessee
- Apr 19 Union troops and fleet occupy For Huger, Virginia
- Apr 21 Bahá'u'lláh, founder of the Bahá'í Faith, enters garden of Rivden near Baghdad. He makes his declaration as a Messenger of God during the 12 days spent there
- Apr 24 Skirmish at Okolona and Birmingham, Mississippi (Grierson's Raid)
- Apr 27 Battle of Streight's raid: Tuscumbia to Cedar Bluff, AL
- Apr 29 Battle of Chancellorsville, Virginia (Fredericksburg, Wilderness Tavern)
Victory in Battle
Apr 30 -5/1] Battle of Snyder's Bluff, Virginia (part of the Vicksburg Campaign of the American Civil War): General Sherman beaten by Confederate forces
William Tecumseh Sherman
- Apr 30 Mexican forces attacked the French Foreign Legion in Hacienda Camarón, Mexico.