William C. Chamberlain was born on December 12, 1845, in Farmington, Pennsylvania, to Nelson and Dimis Chamberlain. His father was a farmer who owned $200 of personal property by 1860. The family lived in Farmington until the 1850s, when they moved to Cameron, New York.
According to an early biographer, “When only a lad of fifteen years his heart became fired with patriotism, which found expression in his service to his country.” He enlisted in the Union army on August 14, 1861, and he mustered in as a private in Company B of the 86th New York Infantry on August 30. He apparently lied about his age, claiming that he was eighteen years old. The regiment took part in the Second Battle of Manassas. He fell ill in the summer of 1862, and he spent several months in Harewood General Hospital in Washington, D.C. Union officials transferred him to a hospital in Rhode Island in November 1862, and he was discharged for disability on January 3, 1863.
He settled in Alma, New York, after leaving the army. According to one biographer, he “purchased a tract of wild, undeveloped land, which he improved, and when it was discovered to be in the oil district he sold it for a large advance upon the price paid.” He married Cornelia White on May 4, 1870, and they had two children: Cora, born around 1873; and Mildred, born around 1878. He applied for a federal pension in March 1882 and eventually received one. They moved to Hambden, Ohio, around 1884. He supported the Republican Party, and he served on the Board of Trustees for Hambden Township. He died of pneumonia in Lake County, Ohio, in 1917.