William Henry Blackwell was born on March 9, 1839, in Kentucky. He eventually moved to Indiana. He enlisted in the Union army on August 7, 1862, and he mustered in as a corporal in Company F of the 79th Indiana Infantry later that day. The regiment took part in the Battle of Perryville and the Battle of Stones River, and Blackwell was discharged on February 14, 1863.
Blackwell settled in Wayne, Indiana, after leaving the army, and he married Corann Vanblaricum there on September 10, 1863. They had at least five children: Harry, born around 1865; Jessie, born around 1866; Alfred, born around 1871; Albert, born around 1876; and Frank, born around 1880. He applied for a federal pension in September 1868 and eventually secured one. He worked as a farmer, and by 1870, he owned $350 of personal property.
He moved to Indianapolis in the early 1900s, and his wife died there on April 1, 1906. He passed away of arteriosclerosis in Indianapolis on March 30, 1922.