According to Wikipedia, Decoration Day was set up shortly after the Civil War by Grand Army of the Republic (GAR) National Commander General John Logan to honor Union soldiers who had died in the conflict. The GAR was an association of former soldiers (and sailors).
By the end of the war in 1865, the practice of decorating the graves of soldiers was widely practiced in the North and South as well. The general called for every GAR Post to celebrate Decoration Day May 30, 1868.
That year there were events held in 183 cemeteries in 27 states and the number of cemeteries rose to 336 the following year.
Michigan made it an official state holiday in 1871 and by 1890 every Northern state had done the same.
Generally, the 100,000 member Women's Relief Corps ran the events.
By 1870, the remains of nearly 300,000 Union soldiers had been moved to 73 National Cemeteries, mostly in the South near battlefields.
A Day Linked Deep in Our History. --Old B-Runner