Nativity of St. John the Baptist is celebrated on June 24, 2018. The Nativity of St. John the Baptist (or Birth of John the Baptist, or Nativity of the Forerunner) is a Christian feast day celebrating the birth of John the Baptist, a prophet who foretold the coming of the Messiah in the person of Jesus, whom he later baptised.
The Nativity of St John the Baptist is one of the oldest festivals of the Christian church, being listed by the Council of Agde in 506 as one of that region's principal festivals, where it was a day of rest and, like Christmas, was celebrated with three Masses: a vigil, at dawn, and at midday.
Beyond the religious commemoration, many regional customs associated with the Nativity of John the Baptist are in fact more related to the concurrent celebration of midsummer which are themselves remnants of pre-Christian pagan midsummer festivals. (With material from: Wikipedia)