Nesmith was born as Mabel Elizabeth Cowart on 3 March 1909 (officially). She always celebrated her birthday on 28 February, and once attempted to legally change her birth certificate. She was the daughter of Mark and Ida Cowart, and grew up in Harlingen, Texas, with her two sisters, Fay and Myrtle, the latter of whom lived to be 100, as did an aunt, Nona. Another aunt, Cora, lived to 103.
Nesmith married her husband, Terry, in 1927, and the couple had three children, including son Gary. She remembered being the first girl in her high school to wear blue jeans, breaking her arm whilst attempting to hand-crank her Ford Model-T, and seeing a television for the first time.
Widowed in 1960, Nesmith later moved to Littleton, Colorado. At the time of her 110th birthday, in addition to her three children, she had six grandchildren, 10 great-grandchildren, and seven great-great-grandchildren. She was in good health aside from arthritis, and enjoyed watching every Broncos game on the television.
Nesmith died on 23 August 2019 at the age of 110 years, 173 days.
Nesmith’s age was verified by Eli Logan and Stefan Maglov, and was validated by LongeviQuest in 25 August 2024.