Sure enough, in Joanne Chiles Eakins' "Missouri Prisoners of War" 1995 book listing in alphabetical order the Missouri military and political prisoners of the St. Louis area prisons is an entry that says:

Private William Hearst of Jefferson County, MO arrested at home on 1 November 1861 and sent to the Alton, Illinois military prison. There is no further disposition of this prisoner shown in this source, and nothing in the remarks column. These National Archives records reflect the Union military ledger giving the general information about each prisoner and are not dossiers or biographies or any other detailed source.

As background, the Union military in Missouri came down hard on southerners who helped to fire railroad bridges in the state after the tragic trainwreck on the Hannibal to St. Joseph Railroad on 3 September 1861. In this instance, the engineer of a train failed to notice that the Platte River Bridge had been partially burned before he drove over it and the resulting collapse threw the train into the abyss, killing 21 and injuring about 40 including women and children and the Kansas City postmaster. From my reading, the Union military made that particular crime subject to the death penalty and this resulted in part during early 1862 to the infamous "no quarter" rule that over the entire guerrilla war in Missouri cost the lives of hundreds on both sides who were denied by both sides fair capture and parole because of that ruling. Ironically, those "bridgeburners" who were given the death penalty all or nearly all had their sentences reduced by higher authority to imprisonment for the duration of the war, similar to William Hearst's sentence.

Sources for the Platte River Bridge disaster:
--"New York Tribune" 12 September 1861;
--St. Louis "Daily Missouri Democrat" of 6 and 10 September 1861;
--"Hannibal Messenger" 12 September 1861;
--"Confession of Willard Francis Hadley," "Missouri Statesman" Columbia, Boone County, 1 July 1864, quoting earlier issue of Jefferson City, "Missouri State Times;"
--Richard S. Brownlee, "Gray Ghosts of the Confederacy," page 24.

Bruce Nichols