Born in Marshall County, Iowa, on October 17, 1858, John A. Plummer was educated in the Iowa public schools, and at the Friends' Academy. He read the law in the office of Hon. J.W. Dorsey, Elko, Nevada, and was admitted to practice in 1886. Plummer served as district attorney there for 2 years. In 1892, he moved to Stockton, California, and was admitted to the California Bar. He engaged in private practice until 1910, when he was appointed Judge of the Superior Court of San Joaquin County. During the 13 years Plummer served on the superior court, none of his decisions was ever reversed by a higher court. In 1923, he was appointed to the Court of Appeal, Third Appellate District. Justice Plummer died in office, October 16, 1938, one day shy of his 80th birthday.