William Wilkinson was born around 1843 in Indiana to John and Eusebia Wilkinson. His father was a farmer who owned $800 of real estate and $700 of personal property by 1860. The family lived in Vermillion, Indiana, until the 1850s, when they moved to Gentry County, Missouri. Wilkinson enlisted in the Union army on September 1, 1862, and he mustered in as a private in Company G of the 35th Missouri Infantry later that day. He eventually earned a promotion to sergeant.
He returned to Missouri after the war, and he married a woman named Elizabeth in the mid-1860s. They had at least six children: Edward, born around 1868; Ora, born around 1871; Rosalie, born around 1873; Frederick, born around 1877; Cooper, born around 1884; and Etta, born around 1892. They lived in Lewis, Missouri, and Wilkinson worked as a laborer. By 1870, he owned $200 of personal property. They moved to Pittsburg, Kansas, in the mid-1870s, and Wilkinson worked as a farmer there.
He applied for a federal pension in September 1891 and eventually secured one. By 1900, they were living in Washington, Kansas, and Wilkinson was working as a railroad laborer. Two decades later, he was working in a grain mill. He died in Kansas around 1926.