Mary Hornor was born on August 20, 1838, in Helena, Arkansas, to John and Elizabeth Hornor. Her father was a merchant who owned $30,000 of real estate and $30,000 of personal property by 1860. She grew up and attended school in Helena, and she married Peter Thweatt around 1870. They had at least four children: Elizabeth, born around 1877; Henrietta, born around 1879; Oscar, born around 1880; and Ree, born around 1883. They lived in Helena, and her husband worked as a lawyer. She died of arteriosclerosis in San Antonio, Texas, on October 30, 1925.