2002 €urozone countries:

€urozone: €uro coins and banknotes first entered circulation in January 2002

Founding states: Austria, Belgium, Cyprus, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, Malta, The Netherlands, Portugal, and Spain.

Also used by formal agreement in non-EU states: Monaco, San Marino and Vatican City.

Montenegro and Kosovo both adopted the euro as their currency in January 2002, but without formal agreement

Joining the €urozone later:
Founding states 2002
Adopted 2002, no agreement
Slovenia 2007, Slovakia 2009, Estonia 2011, Latvia 2014