Memorial Day, originally called Decoration Day, is a day of remembrance for those who died in our nation's service. The preferred name for the holiday gradually changed from "Decoration Day" to "Memorial Day", which was first used in 1882.
Decoration Day was officially proclaimed on 5 May 1868 to honor Union and Confederate soldiers by General John Logan, national commander of the Grand Army of the Republic (an organization for Northern Civil War veterans), in his General Order No. 11, and was first observed on 30 May 1868, when flowers were placed on the graves of Union and Confederate soldiers at Arlington National Cemetery. The date was chosen because it was not the anniversary of a battle.
The holiday changed after World War 1 from honoring just those who died fighting in the Civil War to honoring Americans who died fighting in any war.
In 1971, Memorial Day was declared a federal national holiday by an act of Congress, and its observance was set on the last Monday in May.