Series consists of records created and/or maintained by companies that comprised the Great Western Railway System. The unused charter of The London And Gore Railroad Company was revived on 29 March 1845 (Upper Canada Statutes, 8 Vic. Cap. 86) though with certain alterations including the name being changed to The Great Western Railroad Company. The name was again altered on 22 April 1853 (Canada Statutes, 16 Vic., Cap. 99) to The Great Western Railway Company. In 1853 and 1854, 229.91 miles of line between Niagara Falls, Hamilton, London and Windsor were opened for traffic. Some 33.19 miles were subsequently added in various locations for a total of 263.10 miles. Although nominally leased to the Great Western, The Galt And Guelph Railway Company (RG30-I-F-2) constructed between 1855 and 1857 was a wholly owned subsidiary.
By the provisions of the Great Western Railway Company's Financial Act, 1871 (Statutes of Canada, 34 Vic. Cap. 44), The Hamilton and Toronto Railway Company (RG30-I-F-3), The Canada Air Line Railway Company (RG30-I-F-4) and The London and Port Sarnia Railway Company (no records at National Archives) amalgamated with The Great Western Railway Company under the latter's name. The London and Port Sarnia Railway Company had 50.85 miles of track running from Komoka to Sarnia.
The line and services of the Wellington, Grey and Bruce Railway Company (RG30-I-F-5) were leased in 1870 and operated by the Great Western from 1872. The Great Western sponsored the London, Huron and Bruce Railway Company (RG30-I-F-6), supervising its construction and leasing it from 1876.
The Brantford, Norfolk and Port Burwell Railway Company (RG30-I-F-7) was also leased and operated from 1878. The London and Port Stanley Railway was leased in 1871, but it passed out of Great Western/Grand Trunk control in 1892, and did not rejoin the C.N.R. system until 1963.
In the United States, the Great Western obtained control through a mortgage in 1857 of the Detroit and Milwaukee Railway Company (RG30-I-F-8-c), and operated the line from 1878, when the name was changed to Detroit, Grand Haven and Milwaukee Railroad Company. The Great Western also has an interest in the Detroit River Tunnel Company (RG30-I-F-9) although no progress appears to have been made in construction.
On 12 August 1882 The Great Western Railway Company, under an agreement of 25 May 1882, amalgamated with The Grand Trunk Railway Company of Canada under the latter's name. The various subsidiaries and controlled lines previously mentioned also came under Grand Trunk control and ownership.