Yamaguchi was born in Kagoshima City, Kagoshima Prefecture on 20 March 1907. Her former samurai family was well-known in her area and was described as “distinguished” by acquaintances.

Yamaguchi later married and had six children, two sons, and four daughters. She was a full-time housewife, while her husband worked in forestry. Her family reported that she always maintained a “dignified posture.”

Following the 1 April 2016 death of Minoe Kageyama, Yamaguchi, then aged 109, became the oldest resident of Miyazaki Prefecture.

Aged 111, Yamaguchi, along with her six children, had eight grandchildren, 11 great-grandchildren, and eight great-great-grandchildren. She claimed that the secret to her longevity was, “I try to think only of the good and am grateful [for] every day.”

Yamaguchi’s daily routines aged 113 included reading books and newspapers. She had a loud and clear voice and was still mentally sharp.

Yamaguchi died in Hyuga, Miyazaki on 6 September 2020 at the age of 113 years, 170 days. She was succeeded as the prefecture’s oldest living person by Hide Hamabe (1908 – 2023).