He remained in the army after the expedition returned, serving in the War of 1812, in which he lost an eye, and fighting in the battle of Lundy's Lane. During the Civil War, Gass at the age of 91 years had to be removed from a recruiting station after he wanted to enlist to fight the rebels. ("Wisdom of History" by J. Rufus Fears). At the age of 60, he married Maria Hamilton, aged 20. She bore seven children (six of whom survived to adulthood) over the remaining 15 years of her life. They settled in Wellsburg, West Virginia, where he died, 99 years of age, the oldest surviving member of the expedition.