On her father's side, she is a descendant of Judge Theodore Sedgwick, Endicott Peabody (the founder of the Groton School), William Ellery (a signer of the Declaration of Independence), Samuel Appleton, John Lathrop (American minister) (1740–1816), of Boston, Massachusetts, and is the great-granddaughter of Henry Dwight Sedgwick III, thus the corresponding niece to his brother Ellery Sedgwick, owner/editor (1908-1938) of The Atlantic Monthly. Sedgwick is also a sister of actor Robert Sedgwick, half-sister of jazz Guitarist Mike Stern, the first cousin once removed of Actress Edie Sedgwick, and a niece of the Writer John Sedgwick. She is also the aunt of R&B/pop singer George Nozuka and his younger singer-songwriter brother Justin Nozuka (their mother, Holly, is Sedgwick's half-sister).