William Henry McMaster (May 10, 1877 – September 14, 1968) was an American politician who served as the tenth Governor of South Dakota from 1921 until 1925.

[9]: 294 In 1920, with Governor Peter Norbeck opting to run for the U.S. Senate rather than seek re-election, McMaster entered the race to succeed him.

He ran for re-election in 1922, and though he faced a similarly split field, his victory was considerably narrower; he won only 45% of the vote.

He defeated incumbent Senator Thomas Sterling in the Republican primary and won a 44% plurality in the ensuing general election against Democratic nominee Ulysses Simpson Grant Cherry and several independent candidates.

[10] At the age of 91 years, McMaster died in Yankton and was interred in Oakwood Cemetery, Dixon, Lee County, Illinois US.