He was a volunteer aide (without rank or commission) on the staff of William "Bull" Nelson at the Battle of Richmond, Kentucky in 1862, where he was reportedly wounded.

In October, he was tasked by General Rosecrans to reopen the Iron Mountain Railroad from St. Louis, Missouri to Pilot Knob.

Emerson resumed his law practice at Ironton, and was appointed to the Judgeship of the Fifteenth Judicial Circuit Court, which he eventually resigned.

In 1890, Emerson met two Scottish orphans, Alexander and Charles Meston, who wanted to manufacture electrical and mechanical devices.

He joined the Missouri Commandery of Military Order of the Loyal Legion of the United States and wrote a history of General Grant's campaign in the Mississippi Valley.