William Henry Mims was born on December 18, 1840, in Tippah County, Georgia, to Charles and Eliza Mims. His father was a clerk who owned $7,500 of real estate and $2,000 of personal property by 1860. Mims grew up and attended school in Columbus, Georgia.
He enlisted in the Confederate army on May 6, 1861, and mustered in as a private in Company A of the 2nd Georgia Infantry Battalion later that day. The regiment took part in the Seven Day’s Battles, the Battle of Fredericksburg, the Battle of Chancellorsville, the Battle of Gettysburg, the Overland Campaign, and the siege of Petersburg. He was wounded on August 16, 1864, near Deep Bottom, Virginia. Union forces captured him late in the war, and he was exchanged on February 13, 1865.
Mims settled in Montgomery, Alabama, after the war and earned a living as a schoolteacher. By 1870, he owned $2,500 of real estate and $800 of personal property. He married Annie Royle around 1876, and they had at least two children: Roy, born around 1876; and William, born around 1880. By 1880, they were living in Chattanooga, Tennessee, and Mims was working as a grocer. They moved to Laredo, Texas, in the late 1800s, and Mims began working as a lawyer. He died in Laredo on December 6, 1920.