Missouri was captured by the Union at the First Battle of Boonville on June 17, 1861.
The First Battle of Boonville
Eleven states seceded from the Union 1860-1861 and formed the Confederate States of America. History, though, is written by the winners and Missouri was labeled, at least after the fact, as a loyal Union state. But one must dig deeper than school textbooks to find the truth.
Barely two months after the first shots were fired at Fort Sumter, the First Battle of Boonville took place on June 17, 1861. While it is listed as a battle, it was, in fact, a scrimmage that lasted less than twenty minutes. In that ever so brief battle, Missouri was captured. For the next four years, the state lived under martial law.
A Historic Marker sits on the site of that famous battle and can be found on Morgan Street, east of Main Street and just before one gets to the Missouri Correctional Center.