Well, I'm not sure when and where the expression originated, but the corn around my family farm has been taller than knee high on the 4th of July as far back as I can remember.
I even have proof!
Here's a photo I found of my dad while going through photos at my grandma's house after she passed away a couple of months ago.
It was taken on July 4, 1986 and my grandma wrote on the back: "Norman and our corn on July 4, 1986."
Here's a photo I took of my dad on July 2nd of this year.
The corn is taller this year probably due to an earlier planting date, lot and lots of rain, better seed genetics and better production practices (like conservation tillage).
Happy 4th of July!
