Samuel Swett Green was born February 20, 1837 in Worcester, Massachusetts. He was descended from four progenitors who were Mayflower passengers. He also traced his descent from Thomas Green who emigrated to Massachusetts Bay about 1635 and settled in Malden. Three direct ancestors and an uncle, brother, and nephew were physicians. His father James was an apothecary, orphaned at six, unschooled after twelve, and his mother was Elizabeth Swett.