James Henry Plummer (19 February 1848 – 10 September 1932) was a Canadian financier, He acquired the Dominion Iron and Steel Company in 1903 and developed it as a major industry before and during the First World War.

[1] He was the namesake of the canal-sized package freighter J. H. Plummer, built in 1903 by Armstrong Whitworth & Company Ltd. at Newcastle-on-Tyne.

This 257-foot, 1,643-ton steamer was owned originally by the Canadian Lake and ocean Navigation Company Ltd., a subsidiary of the McKenzie and Mann Group.

[2][3] In 1903 Plummer acquired control of the Dominion Iron and Steel Company Ltd. (DISCO) from James Ross of Montreal, who in turn had purchased it from the Henry Melville Whitney syndicate of Boston, Massachusetts, in 1901.

[4] In 1919 Plummer negotiated the sale of DOMCO and DISCO to a syndicate of British investors led by Roy M. Wolvin of Montreal.