William Cowper Smith (1843 – 5 March 1911) was a Liberal Partymember of parliament in New Zealand.
He represented the Waipawa electorate from 1881 to 1887, then the Woodville electorate from 1887 to 1890 (the electorate only existed for those three years), then the Waipawa electorate again from 1890 to 1893, when he retired.
On 13 December 1895, he was appointed to the Legislative Council. At the expiry of the seven-year terms, he was reappointed on 13 December 1902 and on 13 December 1909. He remained a member until his death on 5 March 1911. For three periods between 1902 and 1908, he was Chairman of Committees of the Legislative Council. He had been the government's preferred candidate as Chairman of Committees in 1901 but W. D. H. Baillie won the election and was confirmed for another (his last) session.