St. John's Day may refer to:
Feasts celebrating the Nativity of Saint John the Baptist:
- January 7, an Eastern Orthodox feast
- June 24, Midsummer Day
- an Eastern Orthodox feast celebrating his birth
- a Roman Catholic, Lutheran and Anglican feast celebrating his birth
- August 29, an Eastern Orthodox feast commemorating his beheading
- September 23
- an Eastern Orthodox feast celebrating his conception
- a Roman Catholic and Lutheran feast celebrating his conception
- Thout 2, a Coptic Orthodox feast
- Dehwa Daimana (Mandaean feast): 1st day of Hiṭia, the 11th month of the Mandaean calendar
Feasts celebrating John the Evangelist
- December 27, a Roman Catholic, Lutheran, and Anglican feast
- May 8, an Eastern Orthodox feast