Origin of Memorial Day: What Memorial Day Means and How It Got Started On 5/31/21 at 3:00 AM EDT Memorial Day is a time to reflect on the sacrifices America's service members have made and to honor those who died serving their country, but it wasn't always called Memorial Day. Memorial Day's origins are rooted in the post-Civil War era when a group of Union army veterans known as the Grand Army of the Republic sought a way to honor fallen service members. Originally called Decoration Day, it was first celebrated on May 5, 1868, and involved decorating the graves of those who died in the Civil War with flowers.