English: A map of the Great Western Railway in Ontario, Canada, as it was at its height in 1879.

The mainline starts in the lower right of the image, at Niagara Falls. It runs west-northwest to Hamilton, then turns due west to London, then west-southwest to Windsor.

A major branch runs to Toronto from a wye junction just northwest of Hamilton. A second splits just west of London and runs to Sarnia.

The wholly-owned Canada Air-Line runs along the bottom of the map from Fort Erie to join the GWR mainline southwest of London at Glencoe. A series of short lines between Niagara Falls and the Air-Line connected the two into a large loop.

Running north-south are two lines that the GWR leased. The eastern one running through Guelph is the Wellington, Grey and Bruce Railway, and the one further west running through London is the London, Huron and Bruce Railway.

The GWR also had trackage rights with the Michigan Central Railroad, which had lines meeting the GWR in Detroit and Buffalo.