Thomas was born in Denver, Hancock County, Illinois, USA, on 24 April 1867, to parents Silas Milton Thomas (1840–1880) and Henrietta J. Groom (1844–1876). She had four siblings: Marietta Thomas (1864–1965), Lucy Liggett (1866–1968), William Sanford Thomas (1869–1961), and Henry Thomas (1876–1879). She grew up on a rural farm. Her father was a postmaster and ran the general store. After both of her parents had passed away by the time she was 13, she moved in with her grandparents in Carthage.
Thomas never married nor had children. In Chicago, she learned the millinery business, and subsequently traveled to Colorado to open her own salon. For many years, she ran a fashionable French millinery salon in Cripple Creek. She expressed how those were the happiest times of her life. She had 18 people working in the salon. Around 1918, she moved to Idaho, where she would eventually own a millinery shop in Twin Falls. At some point, she, along with her two sisters, possessed a fruit farm along the Snake River. She later owned a business in Los Angeles area, where she worked until she was forced to retire at the age of 98.
Before her retirement, she sold her estate in Los Angeles. Before moving into a retirement center, she had fallen and broken her hip. Around 1974, she moved into Alderwood Manor Convalescent Home in San Gabriel. When asked about the secret of her longevity, she explained that despite being constantly aware of life’s challenges and disasters, she has never allowed them to gain the upper hand. In November 1980, she was recognized by the Guinness Book of Records as the oldest person ever. At that time, she expressed that she didn’t know why God had granted her such a long life, but she was prepared to remain until He was ready and willing to depart when He called.
Thomas passed away in San Gabriel, Los Angeles County, California, USA, on 22 January 1981.