R-S
- Jack Richardson, C.M., award-winning record producer, Lifetime Achievement Juno Award recipient, Order of Canada recipient, and educator at Fanshawe College
- Michael Riley, television actor
- John P. Robarts, premier of Ontario, 1961–1971
- Vic Roschkov Sr., newspaper editorial cartoonist/illustrator
- J. Philippe Rushton, researcher and academician at University of Western Ontario
- Craig Simpson, former NHL hockey player and coach
- Dave Simpson, former player with London Knights and current professor at the Richard Ivey School of Business
- Shad, hip-hop musician
- Nick Shaw, musician
- David Shore, writer or producer for the television program House
- Meaghan Smith, Singer-songwriter
- Timothy Snelgrove, founder of Timothy's World Coffee
- Ross Somerville, six-time Canadian Amateur Championship winner in golf, first Canadian to win U.S. Amateur in 1932
- Jude St. John, veteran, all-star player with Toronto Argonauts
- Lara St. John, violinist, sister of Scott St. John
- Scott St. John, violinist/violist, brother of Lara St. John
- Jonny Staub, radio personality
- Barry Steers, Canadian Ambassador to Brazil (1971–1976), High Commissioner to Bermuda (1976–1979), Ambassador to Japan (1981–1989)
- Janaya Stephens, actress, star of the Left Behind movie series
- Adam Stern, Major League Baseball player with the Baltimore Orioles
- Sam Stout, Ultimate Fighting Championship competitor
- David Suzuki, geneticist, environmentalist, writer and broadcaster
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