Joshua Glover was a fugitive slave from St. Louis, Missouri, who sought asylum in Racine, Wisconsin, in 1852. Upon learning his whereabouts in 1854, slave owner Bennami Garland attempted to use the Fugitive Slave Act to recover him. Glover was captured and taken to a Milwaukee jail. On March 18, 1854 a mob incited by Sherman Booth broke into the jail and rescued Glover, who was taken secretly back to Racine, from where he traveled by boat to Canada. He joined the prominent abolitionist movement in Toronto, and spent the remainder of his life in Etobicoke, Ontario, working at Montgomery's Inn.
The rescue of Glover and the federal government's subsequent attempt to prosecute Booth helped to galvanize the abolitionist movement in the state. Eventually, through the state Supreme Court, Wisconsin declared that the Fugitive Slave Act was unconstitutional, the only state to do so.
A Wisconsin Historical Marker at Cathedral Square Park in Milwaukee marks the site of the original court house and jail where Joshua Glover was imprisoned by federal marshals, and later rescued by a mob of 5,000 people. Efforts are underway to create a park monument which meets the National Park Service's requirements for an official National Underground Railroad Network to Freedom site.