In a land area of 1,950 square kilometres, the diocese of Quilon comprises major part of the civil district of Kollam, the taluk of Karthikappally and portions of Mavelikkara and Chengannur. A small portion of Pathanamthitta district (Parumala) also falls within the diocese of Quilon.
Malayalam and English are in use in the territory.
The diocese enjoys all four types of climate such as winter, summer, southwest monsoon and northeast monsoon.
The winter season sets in during December and continues till February-end. The summer season starts in February and continues till May. The southwest monsoon begins either in the end of May or in the beginning of June and fades out by September. The northeast monsoon commences in October. Topography
Quilon diocese also known as Kollam diocese is situated on the southwest coast of India. The district is bound on the north by Alappuzha diocese, northeast by the Pathanamthitta district, on the east by Thirunelveli district of Tamil Nadu, on the south by Thiruvananthapuram district and on the west by the Arabian Sea.