Young Whitlock was born on August 6, 1843 in Illinois to James R. Whitlock and Eliza Ann Swepson. His father died around 1847. Whitlock grew up and attended school in Marshall, Illinois, before starting work as a clerk. He enlisted in the Union army on August 15, 1862, and mustered into Company K of the 130th Illinois Infantry on October 25. The army eventually transferred him to Company K of the 77th Illinois Infantry. According to his miliary service records, he was 5 feet, 6 inches tall, with dark hair and black eyes. He was stationed in Louisiana, and he helped recruit an African American regiment in the fall of 1863. He rejoined his regiment in early 1864, and he was captured by Confederate forces that April. He spent the next fourteen months in a prisoner of war camp in Texas.
Whitlock returned to Marshall after the war and began work as a merchant and grocer. He married Florence Bartlett on November 18, 1868, and their son Swepson was born around 1870. That year, he reported $12,000 of real estate and $2,000 of personal property. His health declined in the 1870s, and he purchased a farm in Atlanta, Georgia, hoping the warmer climate would help him recover. According to a local writer, however, he found the “climate uncongenial,” and he “was brought back here [to Marshall] to die among his friends.” He passed away on October 9, 1881.