Orrin Almiron Montgomery was probably born around 1834 in Vermont to Henry and Betsey Montgomery. His father was a laborer who owned $200 of real estate by 1850. He grew up and attended school in Pownal, Vermont, and by the early 1850s, he was living in North Adams, Massachusetts.
He married Rachel Shattuck on April 1, 1854, and they had two children: William, born on February 3, 1855; and Louisa Abigail, born on July 18, 1856. They lived in Pownal. He enlisted in the Union army on July 21, 1862, and he mustered in as a private in Company E of the 10th Vermont Infantry on September 1. The regiment took part in the Overland Campaign. Confederate forces captured him on June 24, 1864, and imprisoned him at Andersonville. He died there of a “disease supposed to be chronic diarrhea” on September 21, 1864.