John Hiram Whitmer was born on April 25, 1843, in Bluffton, Indiana, to Michael and Volumnia Whitmer. His father was a farmer who owned $2,000 of real estate and $1,000 of personal property by 1860. He grew up and attended school in Bluffton, and by 1860, he was working as a farmer.
He enlisted in the Union army on December 13, 1861, and he mustered in as a sergeant in Company H of the 47th Indiana Infantry. The regiment took part in the Vicksburg campaign.
He settled in Burr Oak, Michigan, after the war and resumed his work as a farmer. He married Cornelia Thompson on August 27, 1867, and they had at least two children: Eva, born around 1868; and May, born around 1869. They also adopted a son named Richard, who was born around 1890. They moved to Sturgis, Michigan, in the late 1800s, and he worked as a lumber dealer there. He also served as president of the National Bank of Sturgis. He died of acute endocarditis in Sturgis on June 10, 1931.