After the end of the war, on January 13, 1866, President Andrew Johnson nominated Smith for appointment to the grade of Brevet brigadier general of volunteers, to rank from March 13, 1865.

At the Battle of Pea Ridge (Elkhorn Tavern), on March 7, 1862, he was severely wounded in the right shoulder and head.

Because he was unfit for field service due to his wounds, the United States Senate did not confirm his appointment as brigadier general of volunteers and it expired on March 4, 1863.

In 1870, President Ulysses S. Grant appointed Smith to the office of collector of internal revenue for the District of New Mexico.

Near the end of the American Civil War in 1865, William ran away from home at age 14 to join his father with the 155th Illinois Infantry Regiment.

[4][5][7] According to Historian Ezra J. Warner Smith was directing the fire of the 1st Iowa Independent Battery Light Artillery[5] when he was shot in the right shoulder and hit in the head by a shell fragment.

[6] Historians William L. Shea and Earl J. Hess described the movement of the 35th Illinois Infantry Regiment down Narrow Ridge to the right of division commander Eugene A. Carr's advanced position on Telegraph Road.

[5] Smith was assigned to recruiting duty after he had recovered enough from the Battle of Pea Ridge to perform limited service.

[5] Smith then was nominated for, and temporarily appointed to, the grade of brigadier general of volunteers in the Union Army by President Abraham Lincoln to rank from September 19, 1862.

[4][5] Since Smith was unfit for field service due to his wounds suffered at Pea Ridge, the United States Senate did not confirm his appointment as brigadier general of volunteers.