Hiram Benjamin Crosby was born in December 1831 in Norwich, Connecticut, to Hiram Crosby and Nancy Carew. His father was a manufacturer who owned $5,000 of personal property in 1860. Hiram grew up and attended school in Norwich, and he graduated from Dartmouth College in 1854. By 1860, he was living in Norwich, and he owned $8,000 of real estate and $1,000 of personal property. He enlisted in the Union army on July 26, 1862, and mustered in as a private in Company C of the 18th Connecticut Infantry. On September 5, 1862, he was promoted to major and transferred to the 21st Connecticut Infantry. The regiment took part in the Battle of Fredericksburg, the Siege of Suffolk, the Battle of Cold Harbor, and the Siege of Petersburg. Crosby was promoted to lieutenant colonel on June 8, 1864, and he mustered out on September 14, 1864.
Crosby married Margaret Ackerman around 1864, and they had at least nine children: Hiram, born around 1872; Margaret, born around 1873; William, born around 1875; John, born around 1878; Helen, born around 1879; Thomas, born around 1880; Constance, born around 1883; Alpheus, born around 1885; and Elizabeth, born around 1891. The family moved to New York, New York, sometime before 1900, and Crosby died there on October 7, 1900.