The answer is ninety years ago today, July 7, 1928 in Missouri by the Chillicothe Baking Company*.
Otto Frederick Rohwedder** of Davenport, Iowa invented the first bread slicing machine and it was this machine that was used by the Chillicothe* Bakery to produce sliced bread. The first batch was sold under the brand name "Kleen Maid Sliced Bread."
Frank Bench, who was 20 years old and going bankrupt, purchased Rohwedder's bread slicing machine and the rest is history. Gustav Papendick bought Rohwedder's second model and improved on it "by devising a way to keep the slices together...to allow the loaves to be wrapped."
In 1974, Rohwedder's daughter, Margaret R. Steinhauer of Albion, Michigan donated her father's bread slicer to the Smithsonian Institution.
*Chillicothe, Missouri, located in Livingston County, has a population of 9515.
**Otto Frederick Rohwedder (1880-1960) was born in Des Moines, Iowa to parents of German descent. He grew up in Davenport where he earned a degree in optics in 1900. OFR, the father of the bread slicing machine, died on the day JFK was elected POTUS.
Lemels N-Mit, "Invention of the Week," www.web.mit.edu/