Elizabeth Tilney was born at Ashwellthorpe Hall sometime before 1445, the only child of Sir Frederick Tilney, of Ashwellthorpe, Norfolk, and Boston, Lincolnshire, and Elizabeth Cheney (1422-1473) of Fen Ditton, Cambridgeshire.
Elizabeth's paternal grandparents were Sir Philip Tilney and Isabel Thorpe, and her maternal grandparents were Sir Laurence Cheney of Fen Ditton and Elizabeth Cockayne, widow of Sir Philip Butler.