Ireland has no official national outfit, so “traditional Irish clothing” can be interpreted as anything from historical clothing to modern day step dancing costumes.
Medieval and Renaissance:
During the Medieval and Renaissance periods, Irish were distinguished for short tunics. Men wore these tunics with woolen jackets, check trews (knee breeches), and mantels (a type of shaggy fringed cloak).Women wore long dresses (usually laced up the front) and headdresses made up of a roll of linen.
Irish step dancing is currently associated with kilts and elaborately embroidered dresses, which people generally mistake for traditional clothing. This is not the case though these heavily embroidered dance dresses date back only to the 1990s.
Many people believe that the kilt is part of historical Irish dress, especially because it’s worn a lot by male step dancers. According to Reconstructing History, the Irish kilt dates back to approximately 1900, when Irish Nationalist Padraic Pearse advised James O’Kelly to wear a kilt instead of trews. Kilts became popular in step-dancing in the 1930s and 1940s which could be the reason why people believe them to be traditional Irish clothing.