 Marsh then became an Indian agent for the Sioux Agency at Fort Snelling, At Fort Snelling, Marsh took a French/Indian mistress named Marguerite Decouteaux, who bore him a son named Charles.Territorial Governor Lewis Cass appointed Marsh to the position of Justice of the Peace in Crawford County (which included what is now southern Wisconsin, northern Illinois, and portions of Iowa and Minnesota), whereupon he became known as "Judge Marsh.