The Kollam Orthodox Diocese, one of the 30 dioceses of the Malankara Orthodox Syrian Church, was created after the Mulanthuruthy Synod in 1876. H.G. Dr. Joseph Mar Dionysius is the Metropolitan of the diocese, whose head office is in Bishop's House, Cross Junction, Kadappakada, Kollam, Kerala, India.

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Kollam is an ancient commercial center and seaport. According to tradition, Thomas the Apostle arrived in the city and founded a church which is now underwater. Kollam is one of the seven dioceses created after the Mulanthuruthi Syrian Christian Association (synod) of 1876, led by Patriarch of Antioch Ignatius Peter IV; the other dioceses are Kottayam, Kandanadu, Angamali, Niranam, Thumpamon, and Kochi. Originally, there were over 30 churches in the diocese.^[1] Dionysious V was its first metropolitan bishop. He was succeeded by Geevarghese Gregorios of Parumala, who also led the Niranam diocese.^[1] Vattasserril Geevarghese, Geevarghese II (when the diocese's head office was in the Kundara seminary), Alexios Mar Thevodosios of Bethany (who became metropolitan in 1938),^[1] Mathews I, and Mathews II followed.^[1]

Mathews I moved the diocese's head office from Kottappuram Seminary in Kottarakkara to Cross Junction, near Kadappakada, where the bishop's house (aramana) and St. Thomas Orthodox Syrian Cathedral were built.^[1] Mathews II was appointed assistant metropolitan in 1985, and became metropolitan in 1991; the following year, there were 130 parishes and 13 churches.^[1] After his death, Didymos I became the diocese's eighth metropolitan. The Thiruvananthapuram Orthodox Diocese was created from the Kollam diocese in 1979, and the Adoor Kadampanad and Kottarakkara Punalur Orthodox Dioceses were created from the Thiruvananthapuram diocese in 2010.

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The diocese has 64 parishes. The Kadeesha Syrian Church in Port Kollam, the tomb of Mar Abo in Thevalakkara, St. Mary's Orthodox Syrian Church in West Kallada, and St. Thomas Orthodox Syrian Church in Kundara are its oldest religious buildings. Kundara Seminary, the Nedumpaikulam St. George Orthodox Syrian Church, and the Nallila Bethel St. George Orthodox Syrian Church are other churches.