Donald James Cowan (born January 3, 1883 Drumbo, Blenheim Township , Oxford County, Ontario - died January 14, 1964 Brantford, Ontario) was a Canadian lawyer and politician. Educated at the University of Toronto and Osgoode Law School, he established a law practice in Port Arthur, Ontario, in 1908. He served three years 1913-1915 as an alderman and two years as mayor 1916-1917. Subsequently he was city solicitor from January 1919 to November 1934. Appointed Crown attorney for Thunder Bay District, Ontario November 1925. He was elected to the Canadian House of Commons as a Conservative September 1926 and again in 1930. During his two terms in Parliament, he was a member of a select committee appointed to study possible amendments and changes to the British North America Act and promoted a Seaway treaty with the United States. In July 1935 he was rewarded by Prime Minister R.B. Bennett with the judgeship of Brant County, Ontario, only the third judge of that county since 1853.