Richard Baxter Loomis was born on March 17, 1832, in Amherst, Massachusetts, to Austin Loomis and Hannah Dickinson. His father was a farmer who owned $3,500 of real estate in 1850. Loomis grew up and attended school in Amherst, and by 1860, he was working as a laborer.
He enlisted in the Union army on August 5, 1861, and he mustered in as a corporal in Company H of the 21st Massachusetts Infantry later that day. The regiment took part in the Second Battle of Bull Run, the Battle of Antietam, the Battle of Fredericksburg, the Overland Campaign, and the siege of Petersburg. He received a gunshot wound to his left side during the siege of Petersburg. As he explained to his brother, "the ball entered about three inches below the heart struck the rib & it appears followed it & came out under my left arm." Union officials consolidated the regiment with the 36th Massachusetts Infantry on October 21, 1864. At some point during the war, he received a gunshot wound to his left side. He mustered out on July 20, 1865.
Loomis returned to Massachusetts after the war. He married Julia Amsden on March 16, 1865, and they had at least five children: Frederick, born around 1866; Osburn, born around 1868; George, born around 1872; Elizabeth, born around 1877; and Abby, born around 1879. They lived in Leverett, Massachusetts, and Loomis earned a living as a farmer. By 1870, he owned $2,500 of real estate and $1,000 of personal property. The family moved to Greenfield, Massachusetts, in the 1880s. He died there of bronchitis on May 20, 1906.