The County of St. Charles was originally called the District of St. Charles and had no definite limits until 1816 to 1818 when neighboring counties were formed. The borders of St. Charles are the same today as they were in 1818.
Cape Girardeau, New Madrid, St. Charles, St. Louis, Ste. Genevieve formed as original districts of Louisiana District of the Indiana Territory. Present day Missouri was a part of the Spanish Louisiana Territory, owned by Spain, until 1805. It then became part of the Louisiana Territory until the Missouri Territory was formed in 1812. The state was formed in 1821 and was much smaller than the territory.