 Sayville station was originally built by the South Side Railroad of Long Island in December 1868, and was the end of the line until April 1869 when the line was extended to Patchogue.From that point until the early 20th century, the station also served as the local post office.At the time, it contained coal sidings, spurs into lumber yards, a freight house west of Greely Avenue, a dairy farm, and even a horse trolley to the Great South Bay owned by the South Shore Traction Company.