William Dillingham (1843-1923) was a Republican who served one term as governor of Vermont (1888-1890) and five terms in the United States Senate (1900-1923). Dillingham was best known as the chairman of the United States Immigration Commission—better known as the Dillingham Commission. Created by the Senate in 1907, it investigated all aspects of the immigration problem in order to formulate recommendations for changes to federal immigration policy.
In 1911, the Dillingham Commission issued its findings. Publishing thousands of pages of research in 41 volumes of reports, it concluded that the recent so-called "new immigration" of Southern and Eastern Europeans posed a serious threat to American culture and society. The Dillingham Commission's findings influenced the restrictive immigration acts ultimately passed by Congress in 1921 and 1924.