National Cheeseburger Day is September 18. On this day, people across the country enjoy the unofficial holiday by dining on a cheeseburger at their favorite restaurant, or by making burgers at home. While nobody is completely sure of the origins of the cheeseburger, some believe that the recipe was created in 1926. Rumor has it that a 16-year-old Lionel Sternberger was working as a fry cook at his father’s sandwich shop when we dropped a slab of American cheese on a hamburger to see what would happen. Ever since, Americans have been enjoying cheeseburgers for decades.