Polly was born in 1778. Polly's father was Rev Joseph Brereton and her mother was <unknown>. She had a brother and three sisters, named Thomas, Kitty, Nancy and Lucy. She was the youngest of the five children. She had a half-brother and two half-sisters, named Joseph, Alethea and Alethea. She died at the age of 18 in 1796 in Nantwich.