Sam graduated from the University of Michigan with a C.E. degree in 1904. As a young man, Sam was keenly interested in his father's business, assisting him with the plans for setting up a mill for the mass production of maple flooring. Sam worked along side his father for many years and upon the death of his father in 1926, took over management of the family's flooring mills. Following the supply of lumber, Sam established a mill in Dollar Bay. It is reported that the Horner enterprises turned out to be a training ground for ambitious men who were later to go into business for themselves. Many, who have been identified in the industry as owners, managers and foremen in other flooring plants, were once protégés of William Horner. Notable among these are Albert Abendroth who operated the first flooring machine in the Reed City plant, and his sons, Walter and Paul who built the Robbins Flooring Company. He is credited for making many improvements in the industry.
Sam died on May 2, 1954 at the age of 77.