Donald James Cowan (January 3, 1883 – January 14, 1964) was a Canadian lawyer and politician. He represented Port Arthur—Thunder Bay in the House of Commons of Canada.
Born in Drumbo, Blenheim Township, Oxford County, Ontario, Cowan was the son of James D. Cowan and Elizabeth Taylor. Educated in Galt, at the University of Toronto and Osgoode Law School, he established a law practice in Port Arthur, Ontario, in 1908. Subsequently, he was city solicitor from January 1919 to November 1934. Cowan was appointed Crown attorney for Thunder Bay District, Ontario, in November 1925. In 1928, he was named King's Counsel.