The Canada Southern Railway (reporting mark CASO) was a railway in southern Ontario, Canada, founded on February 28, 1868 as the Erie and Niagara Extension Railway. It adopted the Canada Southern Railway name on December 24, 1869. In 1904 the railway was leased to the Michigan Central Railroad for 99 years; in 1929 it was subleased to the New York Central Railroad for 999 years. Its successors Penn Central (formed 1968) and Conrail (formed 1976) later exercised control.
On April 30, 1985, the Canadian National Railway and Canadian Pacific Railway jointly purchased the former CASO from Conrail in order to acquire the Michigan Central Railway Tunnel and the Suspension Bridge at Niagara Falls.[1]
The CASO rarely operated its own rolling stock after acquisition, and its reporting mark was abolished in 1977.