William Henry Parker (born May 5, 1847) was a Republican politician who represented the state of South Dakota in the United States House of Representatives in the early twentieth century. Serving as a Representative for South Dakota’s at-large district (designated here as district “-1”), he held federal office during a single term in Congress.

Parker’s congressional service began on December 2, 1907, and concluded on March 3, 1909. During this period, he served as a member of the U.S. House of Representatives, identified in historical records by the Biographical Directory of the United States Congress under the bioguide ID P000073. Although specific committee assignments, office contact details, and additional roles are not recorded in the available metadata, his tenure places him among the early federal lawmakers representing South Dakota following its admission to the Union.