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- James Wolcott Wadsworth Jr, New York senator from 1915–1927
- O.Z. Whitehead, well-known character actor
- Karl Wiedergott, actor, best known for doing voices in the American television show The Simpsons. His father Fritz was the longtime athletic director at the school
- Sean Wilsey, (did not graduate) memoirist
- Robert Winthrop, conservationist pioneer & former president of Ducks Unlimited
- Chalmers B. Wood, senior Foreign Service Officer and adviser to South Vietnamese government
Read more about this topic: List Of St. Mark's School (Massachusetts) Alumni