Saint Swithin or Swithun (died 862) was an Anglo-Saxon bishop of Winchester, after whom is named a British weather lore proverb.
Saint Swithin or variant spellings may also refer to:
- Saint Swithun in popular culture
- Saint Swithun Wells, executed during the reign of Elizabeth I of England (died 1591)
- Eliza Gutch (1840–1931), who wrote to Notes and Queries under the pseudonym St Swithin