The world's longest thank-you note contains roughly 270,000 signatures and spans 420 meters, meaning it would stand taller than the Empire State Building if it were unfurled next to the iconic landmark, The Great Big Story noted in a video published last week.
The note, called the Morpeth Roll, was created in 1841 by grateful Ireland residents who wanted to send Lord Viscount Morpeth a thank-you note upon his retirement as chief secretary for Ireland.
Sheets of paper were pasted together as the list grew in size, and was eventually rolled around a spool in a box at Castle Howard in Yorkshire.
This kept the document safe during the Great Famine in 1845, during which most 19th-century Irish census records were destroyed, Ancestry.com noted.
It has since been digitized and researchers are studying its contents, which includes the signature of a distant relative of Prince William and Prince Harry, Mental Floss reported.
The roll also contains the residential location and street information for some of the records, which can now be accessed in a keyword search on a digital database.
The historic document has become an important resource for genealogists who have been working to trace the Irish ancestry of people to the 19th century.
They have found several notable signatories in the list, including Augustus Frederick Fitzgerald, the 3rd Duke of Leinster, as well as Daniel O'Connell, who successfully campaigned for Catholic emancipation, and Charles Bianconi, who revolutionized public transport in Ireland, according to Maynooth University in Ireland.