Santos Fierro was born in Santa Barbara, Chihuahua, Mexico on 23 July 1913. In 1916, she moved with her family to El Paso, Texas, USA, where she has lived ever since. She attended school until the fourth grade, and eventually found work in a local hospital, before later being employed by the school district. Her family struggled during the Great Depression, and survived off of food stamps for some time before regaining financial security. In 1938, she married Andres Fierro, and had five children before her husband’s death in 1966. For a few years, she lived in Smeltertown, a residential community in El Paso which housed workers of the ASARCO copper smelter company and their families. She has cited her faith in God, in addition to her large, supportive family, as important factors in her longevity.

Santos Fierro currently resides in El Paso, Texas, USA, at the age of 110.