Yes, it exists.
And apparently it is a real thing that has been around for a while and isn't just about scoring a free donut at Dunkin Donuts once a year (which you really can).
I personally wrote about this last year, describing it as a BS holiday to reward lazy Americans with another reason to be fat (for free, no less). This year I have learned more including the fact that it is a floating holiday...
Click "Read More" to learn more about this sweet holiday.
This holiday is a floater and is celebrated on the 1st Friday in June (last year it was on June 1st).
The origins of this holiday go back to World War I when members of the Salvation Army were sent to France. The volunteers made and distributed donuts to soldiers on the front lines.
During the Great Depression, the "holiday" (YES, I used quotation marks, 'cause I still think is a BS holiday) was celebrated for the first time and the sale of donuts was used as a fundraiser for the Salvation Army.
There is plenty more background on National Donut Day but I refuse to write more from any source (I learned shit from NBC, Huffington Post and checked out Wikipedia) because, as noted, I think this "holiday" was just cooked up...see what I did there??