William Henry Dieterich (March 31, 1876 – October 12, 1940) was an American lawyer and Democratic politician from Illinois.

After graduating from Kennedy Business College in 1897 and Northern Indiana Law School in 1901, Dieterich was admitted to the bar and began to practice in Rushville, Illinois.

[1] In 1911 he moved to Chicago, and then in 1912 to Beardstown, Illinois, in Cass County, adjacent to Schuyler, where he continued his law practice.

[1] In 1916, he was elected to the Illinois House of Representatives, and re-elected in 1918, serving from 1917 to 1921.

[1] In 1930, he was elected U.S. Representative from one of Illinois' two at-large seats, finishing ahead of both Republicans and the other Democrat.