Portal:United States/Anniversaries/September/September 3
- 1777 – American Revolutionary War: During the Battle of Cooch's Bridge, the Flag of the United States is flown in battle for the first time.
- 1812 – Twenty-four settlers are killed in the Pigeon Roost Massacre in Indiana.
- 1855 – American Indian Wars: In Nebraska, 700 soldiers under United States General William S. Harney avenge the Grattan massacre by attacking a Sioux village and killing 100 men, women and children.
- 1925 – USS Shenandoah, the United States' first American-built rigid airship, was destroyed in a squall line over Noble County, Ohio. Fourteen of her 42-man crew perished, including her commander, Zachary Lansdowne.
- 1976 – Viking program: The American Viking 2 spacecraft lands at Utopia Planitia on Mars.
- 2016 – The U.S. and China, together responsible for 40% of the world's carbon emissions, both formally ratify the Paris global climate agreement.