What is the origin of "tall tale"?
Here's a possible early example from The American Museum for February, 1788:
A 1752 printing of William Shakespeare's Julius Caesar includes tall-tale:
Modern copies render this as:
You speak to Casca, and to such a man
That is no fleering tell-tale.
So the 1752 was probably a typo, but could the mistake have been influenced by the existence of tall-tale?
The same applies to this 1714 printing of The Life and Death of Richard III:
Ngrams show usage since around the right time
and the term definitively has its place in American short story, which was one of Mark Twain's playgrounds. However searching through Mark Twain's writings, gave no results so I wonder if it could have been him.
Wikipedia references points to several interesting sites; tall-tale postcards starting at 1908.