James H. Thatcher was born around 1840 in Wayne County, New York, to Cyrus and Mercy Thatcher. His father was a farmer who owned $2,500 of real estate and $827 of personal property by 1860. He grew up and attended school in Ontario, New York.
Thatcher enlisted in the Union army on August 8, 1862, and he mustered in as a private in Battery B of the 9th New York Heavy Artillery six days later. The regiment spent the next year and a half defending Washington, D.C., and it took part in the Overland Campaign, the Shenandoah Valley campaign of 1864, the siege of Petersburg, and the Appomattox campaign. Thatcher was promoted to corporal in February 1864 and to sergeant in January 1865, and he mustered out in Washington, D.C, on July 6, 1865.
Thatcher settled in Webster, New York, after the war and earned a living as a farmer. He married Frances Fox sometime in the late 1860s, and they apparently had no children. They lived in Frances’ father’s household until at least 1880. He died in New York in 1897.