McDonough Wickliffe Willoughby was born on May 22, 1841, in Madison County, Illinois, to James Goforth Willoughby and Mary J. Gates.
He enlisted in the Union army on October 10, 1861, and he mustered in as a private in Company D of the 4th Minnesota Infantry. The regiment took part in the siege of Corinth and the Vicksburg campaign. He mustered out on October 11, 1864.
He settled in Rosamond, Illinois, after the war, and he earned a living as a butcher. He married Lavina Anderson on February 7, 1866, and they had at least two children: Mary, born around 1867; and Luella, born around 1869. By 1870, they owned $600 of real estate. They moved to Girard, Kansas, around 1874, and Willoughby worked as a carpenter there. His wife died on November 26, 1880. He applied for a federal pension in September 1890 and eventually secured one.
He was admitted to the National Home for Disabled Volunteer Soldiers in Leavenworth, Kansas, in April 1893. He was discharged in 1902, but he was readmitted in November 1906. He died of carcinoma in Leavenworth on March 14, 1914.