Nielsen was born on 9 June 1865, the seventh of twelve children in a poor peasant family, at Sortelung near Nørre Lyndelse, south of Odense on the island of Funen. His father, Niels Jørgensen, was a house painter and traditional musician who, with his abilities as a fiddler and cornet player, was in strong demand for local celebrations. Nielsen described his childhood in his autobiography ("My Childhood on Funen"). His mother, whom he recalls singing folk songs during his childhood, came from a well-to-do family of sea captains, while one of his half-uncles, Hans Andersen (1837–1881), was a talented musician.