Natchez, MS Great Natchez Tornado, May 1840
The Great Natchez Tornado hit Natchez, Mississippi on May 7, 1840. It is the second deadliest single tornado in United States history, killing 317 people (the only tornado in the United States to have killed more people was the Tri-State Tornado). It is also one of the few tornadoes to have killed more people than it injured: only 109 were injured.
The tornado formed southwest of Natchez and moved northeast along the Mississippi River. It then moved into the town of Natchez and destroyed many buildings. The final death toll was 48 on land and 269 on the river, mostly from the sinking of flatboats. The death toll is slightly disputed because of the land death toll of 48. It is believed that people died on plantations, and since this was pre-Civil War Mississippi, slave deaths weren't usually counted.
From Wikipedia - Great Natchez Tornado
Read articles about the tornado.