William Duncan Connor (March 24, 1864 – November 20, 1944) was a Canadian-born American politician and the 20th Lieutenant Governor of Wisconsin from 1907–1909.

Born near Stratford, Canada West, Connor moved with his parents from Canada to a farm in Auburndale, Wisconsin in 1872. He attended the State Normal School (now the University of Wisconsin–Oshkosh) in Oshkosh, Wisconsin for two years.

William D. “W.D.” Connor moved to Marshfield, Wisconsin in 1895, and became a successful lumberman and real estate investor in the Pacific Northwest. He established the towns of Laona, Wisconsin, Stratford, Wisconsin, and Connorville, Michigan (originally company towns) in the course of growing his lumber business. Connor is credited with establishing the practice of sustainable forestry. He also tirelessly pursued modern lumber technologies.

Very involved in politics and public service, he served for twenty years as a member of the Wood County Board of Supervisors, and was twice elected chairman. In 1892, 1894, 1896, 1902 and 1904 he was elected a delegate to the Republican State Convention and in 1904 he was also elected one of the four (progressive) delegates-at-large to the National Republican Convention, by the regular Republican State Convention. This was the controversial 'gymnasium convention' that looms large in the history of the progressive movement in Wisconsin.

According to the Dictionary of Wisconsin Biography:

He was at first identified with the Robert M. La Follette wing of the party. In the 1904 progressive-stalwart split, Connor was chosen by the "gymnasium convention" as one of the progressive delegates to the Republican national convention. Although the national convention refused to accept the credentials of the Progressive delegation, the La Follette forces were recognized as the legal Republican ticket by the state supreme court (1904) and Connor became chairman of the Republican state central committee. (1904-1908).

Connor was elected as a Republican to the office of Lieutenant Governor in 1906; receiving 174,750 votes against 104,398 for Michael F. Blenski (Democratic), 25,036 for William Kaufmann (Social Democrats), 8,724 for August F. Fehlandt (Progressive) and 510 for John Veirthaler (Socialist Labor). He served as twentieth Lieutenant Governor of Wisconsin from January 7, 1907 - January 4, 1909, but had a significant falling-out with the Governor Robert La Follette.

William Duncan Connor was a prolific legislator during his time in the Wisconsin State Assembly, sponsoring or co-sponsoring a wide variety of bills aimed at advancing the interests of his constituents and the state as a whole. Some of his most notable pieces of legislation include: Women's Suffrage: Connor was a strong supporter of women's right to vote. Education: Connor was a strong advocate for public education and sponsored several bills aimed at improving the state's school system. In particular, he pushed for increased funding for rural schools and advocated for the creation of a state board of education.