Orson R. Thornton was born around 1846 in Warren County, Kentucky, to William and Isabella Thornton. His father was a Baptist minister who owned $3,000 of real estate and $1,200 of personal property by 1860. The family lived in Warren County until the 1850s, when they moved to Perry County, Illinois.
Thornton enlisted in the Union army on December 8, 1863, and he mustered in as a private in Company A of the 81st Illinois Infantry on December 25. According to his service records, he was 5 feet, 7 inches tall, with light hair and blue eyes. He was killed in action near Guntown, Mississippi, on June 10, 1864.