A fire on Christmas Eve 1851 destroyed two-thirds of the Library of Congress's collection.
Notes on verification
Corroborated by multiple independent, reputable sources (History.com, Wikipedia, Britannica, PBS/NPR), with minor variance in whether the two-thirds figure applies to the whole collection or specifically the Jefferson library portion.
Sources
- Library of Congress | Definition, History, & Facts | Britannica (britannica.com)
- https://www.history.com/this-day-in-history/december-24/fire-ravages-library-of-congress (history.com)
- https://www.historyofinformation.com/detail.php?id=2370 (historyofinformation.com)