Benjamin Hirum Thayer was born on August 1, 1828 in Wayne County, New York, the eighth child of Isaac and Mary (Gallup) Thayer. His maternal grandfather, Benjamin Gallup, was a Revolutionary War veteran who died in 1841 at the advanced age of 102 years.

Benjamin accompanied his family to Michigan in 1839, settling at first in Livingston County. He soon went to Detroit, remaining there six or seven years, then settled in Monroe County. His occupation was that of a carpenter and joiner.

On December 4, 1861 he enlisted as a Private and was mustered December 8, 1861 into Company F, 1st Michigan Engineers & Mechanics. He was described as age 32, height 5’ 8” with light complexion, hazel eyes, and dark hair. Benjamin was part of the regiment’s second detachment, consisting of Companies C, F, and G, which was assigned to General Thomas at Lebanon, Kentucky.

Benjamin participated in the battles of Mill Springs, Perryville, and elsewhere. On April 1, 1862, while on a march from Nashville to Shiloh, the unfurling of the regimental flag frightened a horse, which was hitched on the rear of a wagon train. The horse jumped upon Benjamin, knocking him down and trampling him, and causing injuries to his head and chest. He spent most of the rest of his time in the service in hospitals and assigned light duty as a nurse and in the Engineers and Mechanics tool department. He was mustered out on October 31, 1864 at Atlanta, Georgia.

He was a member of the Methodist Episcopal church and the Grand Army of the Republic (GAR). He was married twice, but had no natural children of his own. However, he did adopt a son, Edwin D. Thayer.

Benjamin H. Thayer died on October 21, 1903 at Petersburg, Michigan, aged 75 years.