Decoration Day was the precursor of the holiday Memorial Day, and was first observed in 1868, following the carnage of the American Civil War.
In early May 1868 Grand Army of the Republic, a nationwide group of veterans of the Union Army, called for a day to remember those who had died in the war.
The G.A.R.'s leader, General John Logan, issued a written call for people to observe a day dedicated to "strewing with flowers, or otherwise decorating the graves of comrades who died in defense of their country during the late rebellion, and whose bodies now lie in almost every city, village, and hamlet church-yard in the land."
On May 30, 1868, Decoration Day was observed at Arlington National Cemetery. Citizens of Washington, D.C., brought wagons of flowers and evergreen boughs to the cemetery and decorated graves. Speeches were given by General Logan and also by James Garfield, a Civil War veteran and future president.
Decoration Day observances were held every year thereafter on May 30th. Over time the name "Memorial Day" came into common use, though the holiday was not officially called that until the 1960s.
By some accounts, the first Decoration Day observance was held by freed slaves in Charleston, South Carolina in May 1865. But the proclamation by General Logan of the G.A.R. in May 1868 is generally regarded as having instituted the observance of Decoration Day.