Josh Hartnett's father is of Irish and German descent, and his mother is of Swedish and Norwegian ancestry.
Josh Hartnett was born on July 21, 1978, in Saint Paul, Minnesota, the United States, to Wendy Anne (Kronstedt) and Daniel Thomas Hartnett. He was raised in Saint Paul by his father and stepmother since the departure of his mother who left the family not long after her divorce. His father was a building manager, and his stepmother, Molly, was an artist. He has three younger siblings from his father's second marriage.