Tornado Alley
Although the official boundaries of Tornado Alley are not clearly defined, its core extends from northern Texas, Oklahoma, Kansas, Nebraska, into South Dakota. States such as Missouri, Iowa, Minnesota, Wisconsin, Illinois, Indiana, and western Ohio are sometimes included in Tornado Alley. Some research suggests that tornadoes are becoming more frequent in the northern parts of Tornado Alley where it reaches the Canadian prairies.
St. Louis tornado history
These tables describe the tornado history for Greater St. Louis. In Missouri, this includes the counties of St. Louis, St. Charles, Franklin, and Jefferson. In Illinois, this includes the counties of Madison, St. Clair, and Monroe. Data for the independent city of St. Louis is not part of these tables unless part of the path of the tornado striking these counties also struck the city.