It's hard to say what the "largest" tornado is. Several have apparently been at least a couple of miles wide, based on the damage they did, but there is no firm way to establish exactly how wide a tornado is. Determining path length is also impossible because there is no way to be sure exactly how many tornadoes are involved. What seems to be one could really be several tornadoes from the same storm. The Guinness Book of World Records lists the Tri-state Tornado that hit Missouri, Illinois and Indiana on March 18, 1925 as having the longest track, 219 miles; the longest time on the ground continuously, 3.5 hours; the first in total area of destruction, covering 164 square miles; and the largest width at over a mile wide. It traveled 219 miles from Ellington, Mo., across southern Illinois to Petersburg, Ind.