The Diocese of Capodistria (also Diocese of Capo d'Istria or Diocese of Koper) (Latin: Dioecesis Iustinopolitanus) was a Roman Catholic diocese located in the town of Koper (Capodistria in Italian) in southwestern Slovenia.
In 1828, it was united aeque principaliter with the Diocese of Trieste to form the Diocese of Trieste e Capodistria.
[1][2] Erected: 530 from the Diocese of Trieste Latin Name: Iustinopolitanus 30 June 1828: United with the Diocese of Trieste to form the Diocese of Trieste e Capodistria Re-established as Diocese of Koper in 1977