What was the first American fast-food restaurant?

The White Castle in Wichita, Kansas, is credited with being the first fast food restaurant, even though the term “fast food” was not yet widely used when it opened in 1921. Though definitions vary, a fast food restaurant is usually distinguished by its speed and efficiency. Customers place their own orders at a centralized counter and take care of picking up their own condiments, utensils, and other necessary accouterments. When it first opened, White Castle served only hamburgers, and that has been the restaurant’s staple ever since.

Source: Delighted Cooking