I know Great Britain recently changed out their pound coins because a significant number were counterfeit.
Over the years, I've gotten a few under weight or just odd cents over the years, but have attributed them to wear or chemical exposure. I don't think that I have handled any counterfeit U.S. circulated coins.
There are known examples of silver coins, even to the quarter, so not meaning silver or numismatic coins.

You know, that state circulation quarter is just such a keeper. Good enough to party like it's 1999.
Has anyone noticed any counterfeit modern circulation U.S. coins during your search?
Silver Monometalism is the most permanent and stable form of money the world has seen. Natural law and history prove silver value is best multiplied by gold and best divided by copper. It is only in this counterfeit currency time when the natural law appears suspended.