Montresor's romantic life has been the subject of much writing. He married at
New York 1 March 1764, Frances Tucker, who was born in New York, 23 April 1744, daughter of Thomas Tucker of
Bermuda, step-daughter of Reverend
Samuel Auchmuty and half-sister of
General Sir Samuel Auchmuty. She returned to England with her husband, and survived him, dying 28 June 1828, at Rosekill,
Kent. By her, he had General Sir Henry Tucker Montresor, John Montresor, General Sir Thomas Gage Montresor, William Robert Montresor (died, a soldier), and daughters Frances Margaret Montresor, Mary Howe Montresor and Mary Lucy Montresor, who married General Sir Frederick William Mulcaster (brother of
William Mulcaster).
In addition to these relationships, he also had other more irregular connections. A surviving letter from Detroit, 1763, mentions the death of an apparent mistress, "poor Nancy", and that he had been "on the Common" since. Likewise, he made a small grant for the support of the child of the daughter of a local English farmer, of which John was the father.
Finally, his name appears broadly as the father of Frances, second wife of
Ethan Allen. Born to a
Mohawk Valley woman on (Ethan Allen would later record)
4 April 1760, Frances was adopted by her mother's later companion,
Crean Brush, one-time secretary of the Assembly of the Colony of New York. As to her paternity, when her daughter
Frances "Fanny" Allen entered
Hôtel-Dieu in 1808, her mother's maiden name was recorded as Montresor. Her tombstone names her Montezuma, while an
1858 history written using family information calls her Frances Montuzan, relating that her father was a British colonel killed in the French and Indian War. Popular opinion makes John Montresor the father of Frances. This has not been in small part due to his role in a popular best-selling novel of the time.