- Sinking of HMHS Llandovery Castle
- Sinking of the SS Caribou
- Sinnisiak
- Sioui Case
- Sioux Narrows-Nestor Falls
- Sir Adam Beck
- Sir Adams George Archibald
- Sir Adolphe-Basile Routhier
- Sir Albert Edward Kemp
- Sir Albert James Smith
- Sir Alexander Campbell
- Sir Alexander Mackenzie (Explorer)
- Sir Alexander Mackenzie (Railway Magnate)
- Sir Alexander Tilloch Galt
- Sir Alfred Bishop Morine
