- Sep 1 2nd day of battle at Jonesboro Georgia, about 3,000 casualties
- Sep 1 Skirmish at Hood evacuated confederates from Atlanta GA
Battle of Atlanta
Sep 2 US Civil War: Union General William T. Sherman captures and occupy Atlanta, Georgia, ending the Atlanta Campaign [1]
- Sep 3 Battle of Berryville, Virginia, Confederate forces retreat in face of Union strength
- Sep 3 US, British, French & Dutch naval officer sails Straits of Simonoseki
- Sep 4 Bread riots in Mobile, Alabama
- Sep 5 Achille François Bazaine becomes Marshall of France.
- Sep 5 British, French & Dutch fleets attack Japan in Shimonoseki Straits
- Sep 16 British Open Men's Golf, Prestwick GC: Tom Morris Sr. wins third title; beats fellow Scot Andrew Strath by 2 strokes
- Sep 16 US Civil War: Battle of Coggin's Point, Virginia (Hampton-Rosser Cattle Raid)
- Sep 17 American Civil War: Grant approves Sheridan's plan for Shenandoah Valley Campaign
- Sep 18 Battle of Martinsburg, Virginia
- Sep 18 Hood's Tennessee campaign begins (also called The Franklin–Nashville Campaign), American Civil War
- Sep 19 Third Battle of Winchester, Virginia [Opequon], large bloody battle with the Union army defeating Confederate force with over 9,000 casualties
- Sep 22 Battle of Fisher's Hill, Virginia - Confederate General Jubal Early Retreats to Brown's Gap after advance by Union army under General Philip Sheridan
- Sep 27 Battle at Pilot Knob (Ft Davidson) Missouri: 1700 killed or injured
Centralia Massacre
Sep 27 Centralia Massacre: Pro-Confederate guerrillas led by William T. Anderson with Jesse James loot Centralia and attack a train on the North Missouri Railroad, executing 24 Union soldiers. Later the same day the guerillas defeat the newly formed 39th Missouri Infantry Regiment, killing 123 of its 147 solders.
- Sep 28 -30) Battle of Fort Harrison Virginia (Chaffin's Farm New Market Heights)
- Sep 29 Battle of Chaffin's Farm and New Market Heights in Henrico County, Virginia
- Sep 30 13 Black soldiers among the first Black soldiers to be honored with US Medal of Honor for leading charges against Confederate fortifications during Battle of New Market Heights, Virginia
- Sep 30 Battle of Preble's Farm Virginia (Poplar Springs Church)
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