It was technically before the US was officially founded (counting from the adoption of the Constitution), but the Continental currency printed by the Continental Congress during the Revolutionary War was inflated to such a degree that a banknote in 1781 had only 1/40 of its original value in 1776, and was finally redeemable at only 1% of its face value in the 1790s, thus leading to the expression "Not worth a Continental".

https://en.wikipedia.org/wiki/Early_American_currency#Contin...

Edit: tried to clarify wording. In 1781, a banknote of a specific denomination was worth only 1/40th of what the same banknote was worth in 1776.