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- Samuel McDonnell (1834–1910), Canadian politician from Nova Scotia
- Sanford N. McDonnell (born 1922), American aviation businessman, nephew of James Smith McDonnell
- Shannon McDonnell (born 1987), Australian rugby league player
- Sophie McDonnell (born 1976), British television presenter
- Sorley Boy MacDonnell (Somhairle Buidh Mac Domhnaill) (1505–1590), Irish clan chieftain of the Clan MacDonnell
- Stephen McDonnell (disambiguation)
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