General John A. Logan. From Wikipedia: Memorial Day.
The official birthplace of Memorial Day is Waterloo, New York. The village was credited with being the birthplace because it observed the day on May 5, 1866, and each year thereafter, and because it is likely that the friendship of General John Murray, a distinguished citizen of Waterloo, and General John A Logan, who led the call for the day to be observed each year and helped spread the event nationwide, was a key factor in its growth.

General Logan had been impressed by the way the South honored their dead with a special day and decided the Union needed a similar day. Reportedly, Logan said that it was most fitting; that the ancients, especially the Greeks, had honored their dead, particularly their heroes, by chaplets of laurel and flowers, and that he intended to issue an order designating a day for decorating the grave of every soldier in the land, and if he could he would have made it a holiday.


Logan had been the principal speaker in a citywide memorial observation on April 29, 1866, at a cemetery in Carbondale, Illinois, an event that likely gave him the idea to make it a national holiday. On May 5, 1868, in his capacity as commander-in-chief of the Grand Army of the Republic, a veterans' organization, Logan issued a proclamation that "Decoration Day" be observed nationwide. It was observed for the first time on May 30 of the same year; the date was chosen because it was not the anniversary of a battle. The tombs of fallen Union soldiers were decorated in remembrance of this day. ...


The alternative name of "Memorial Day" was first used in 1882, but did not become more common until after World War II, and was not declared the official name by Federal law until 1967. On June 28, 1968, the United States Congress passed the Uniform Holidays Bill, which moved four holidays from their traditional dates to a specified Monday in order to create a convenient three-day weekend.