Wow, this is interesting.

Deadliest Days in American History

1. September 8-9, 1900, Galveston Hurricane 8,000
2. September 17, 1862, Battle of Antietam 4,300
3. September 11, 2001, terrorist attacks 2,992
4. April 18-21, 1906, San Francisco Earthquake and Fire 2,500
5. September 16, 1928, Lake Okeechobee Hurricane 2,500