Yes, Dublin is in the European Union. Dublin is the capital city of Ireland, and Ireland has been a member of the European Union since 1973. As a member state, Ireland, and therefore Dublin, is part of the EU’s political and economic framework.
Being in the EU means that Dublin benefits from various EU policies, including free trade, freedom of movement for EU citizens, and access to EU funding and programs. Additionally, the Euro is the official currency in Dublin, as Ireland is part of the Eurozone.