North was descended from the 1st Earl of Sandwich and was related to Samuel Pepys and the 3rd Earl of Bute. He at times had a slightly turbulent relationship with his father Francis North, 1st Earl of Guilford, yet they were very close. In his early years the family was not wealthy, though their situation improved in 1735 when his father inherited property from his cousin. Frederick's mother, Lady Lucy Montagu, died in 1734. His father remarried, but his stepmother, Elizabeth North, died in 1745, when Frederick was thirteen. One of his stepbrothers was Lord Dartmouth, who remained a close friend for life.