William Williamson (October 7, 1875 – July 15, 1972) was an American teacher, lawyer, and judge who served as a U.S. Representative from South Dakota's 3rd congressional district from 1921 to 1933, as a member of the Republican Party.

William Williamson was born near New Sharon in Mahaska County, Iowa, to the Norwegian immigrants Vilum Vilumson Halleland and Maren Ingebretsdatter Erland, who had left their homeplace in Skjold near Haugesund in 1872.

He began his law practice in Oacoma, South Dakota in Lyman County in that same year.

[3][4] He resumed his law practice in Rapid City, and was special assistant attorney general of South Dakota and assigned as general counsel for the Public Utilities Commission 1939–1951, and also the Department of Insurance of South Dakota.

He is buried in Pine Lawn Cemetery, Rapid City, South Dakota.