The Finnish name for the Midsummer holiday after Christianization is Juhannus.
Before Christian influence, Finnish Midsummer was associated with Ukko, a prominent deity in pre-Christian Finnish tradition, and was called Ukon juhla, or “Ukko’s celebration.” The Christian calendar connected the celebration with Saint John the Baptist, whose Finnish name is Johannes Kastaja; Juhannus developed from that association.
Finnish Juhannus is marked by lakeside or seaside bonfires called kokko, birch branches placed near doors, sauna, communal meals and gatherings at summer cottages. The holiday is also famous for the “white night”: near the Arctic Circle, darkness is brief and some northern areas experience the midnight sun.
A common mix-up is treating Juhannus as the fixed date of 24 June. Finland moved the official holiday to a Saturday between 20 and 26 June in 1955, although celebrations often begin on Friday evening. Swedish-speaking Finns may also use Johannes or Johanni, but Juhannus is the standard Finnish name.