The Flushing and North Side Railroad was a former railroad on Long Island built by Conrad Poppenhusen as a replacement for the former New York and Flushing Railroad. The railroad was established in 1868, was merged with the Central Railroad of Long Island in 1874 to form the , and was finally acquired by the Long Island Rail Road in 1876. Today the main line is known as the Port Washington Branch of the Long Island Rail Road.