2012 Croatian European Union membership referendum
A referendum on the EU accession of the Republic of Croatia was held on 22 January 2012. Croatia finished accession (membership) negotiations on 30 June 2011 and signed the Treaty of Accession on 9 December 2011, setting it on course to become the bloc's 28th member state.
Source: Wikipedia — 2012 Croatian European Union membership referendum (CC BY-SA 4.0)