In addition to the children he sired with Mary White, Morris fathered a daughter, Polly, who was born out of wedlock around 1763. Morris supported Polly financially and remained in contact with her throughout her adult life. Morris also supported a younger half-brother, Thomas, whom Morris's father had sired out of wedlock shortly before his own death. Thomas eventually became a partner in Morris's shipping firm. Mary's brother, William White, was ordained as an Episcopal priest and served as the Senate chaplain.