William M. Kerr was born on December 23, 1843, in Gresham, Pennsylvania, to Andrew and Mary Kerr. His father was a farmer who owned $2,000 of real estate and $500 of personal property by 1860. Kerr grew up and attended school in Oil Creek, Pennsylvania. He enlisted in the Union army on August 9, 1862, and he mustered in as a private in Company G of the 127th Pennsylvania Infantry later that day. The regiment took part in the Battle of Fredericksburg and the Battle of Chancellorsville, and Kerr mustered out on May 29, 1863.
Kerr returned to Oil Creek after leaving the army, and he married a woman named Nancy around 1865. They had at least three children: Mary, born around 1868; Eva, born around 1872; and Stella, born around 1881. He worked as an oil well driller, and by 1870, he owned $5,000 of real estate and $2,000 of personal property. He also employed at least two white laborers. By 1880, he was working as a farmer. He died of heart disease in Titusville, Pennsylvania, on April 4, 1908.