From the official Virginia state government records (www1.va.gov/opa/speceven/memday/history.asp) , the following historical account of the first Memorial Day observances. Interestingly, as one might suppose, it was the Southerners respectfully mournfully memorializing their Confederate men who died defending their homeland who first began the tradition and this was adopted by communities in the North. Of course separate Confederate Memorial Day observances were subsequently adopted throughout the Southern states upon the coopting of the memorial observances by the Yankees.
The most widely accepted first observance of a Memorial Day was held "in Columbus, Miss., April 25, 1866, when a group of women visited a cemetery to decorate the graves of Confederate soldiers who had fallen in battle at Shiloh. Nearby were the graves of Union soldiers, neglected because they were the enemy. Disturbed at the sight of the bare graves, the women placed some of their flowers on those graves, as well."
"Today, cities in the North and the South claim to be the birthplace of Memorial Day in 1866. Both Macon and Columbus, Ga., claim the title, as well as Richmond, Va. The village of Boalsburg, Pa., claims it began there two years earlier. A stone in a Carbondale, Ill., cemetery carries the statement that the first Decoration Day ceremony took place there on April 29, 1866."
"In 1966, Congress and President Lyndon Johnson declared Waterloo, N.Y., the “birthplace” of Memorial Day. There, a ceremony on May 5, 1866, honored local veterans who had fought in the Civil War. Businesses closed and residents flew flags at half-staff. Supporters of Waterloo’s claim say earlier observances in other places were either informal, not community-wide or one-time events."
"It was not until after World War I, however, that the day was expanded to honor those who have died in all American wars. In 1971, Memorial Day was declared a national holiday by an act of Congress, though it is still often called Decoration Day. It was then also placed on the last Monday in May, as were some other federal holidays."