William Warren was a resident of Mansfield on July 21, 1862 when he enlisted as a Private in Co. F of the 18th Regiment Connecticut Volunteer Infantry; he was captured June 15, 1863, Winchester, Virginia, paroled July 14, 1863 and mustered out June 27, 1865.

He was born about 1844 in Coventry, Connecticut to Ziba and Phebe C. (Balch) Warren. In the 1860 U.S. census in Mansfield, he is an 18 year old in the household of Ziba Warren. William Warren married Esther King about 1871. Children include Alice Warren, born about 1874. He returned to Mansfield after his Civil War service and worked as a farm laborer.

On February 2, 1881, he applied for an invalid pension under No. 416,716 that was granted under certificate No. 438,138.

William Warren was a farm hand of Augustus Storrs on May 9, 1883 when he had a serious accident while hitching up a pair of young cattle. The May 16, 1883 issue of the Willimantic Chronicle stated that the cattle bolted before he could extricate himself from the harness. In the article, the correspondent remembered his previous conversations with William Warren about his experiences as a prisoner of war. He was captured with thousands of others at the Battle of Winchester and endured a dry and dusty march down the Shenadoah Valley in Virginia; captors and captives alike were parched with thirst as the wells were drained and water was unavailable. A second article in the May 23, 1883 issue of the Willimantic Chronicle stated that William Warren had died of his injuries and left a wife and daughter.

William Warren died on May 17, 1883 in Mansfield; he is buried at the New Storrs Cemetery in Mansfield.