In a land area of 15222 square kilometers, the diocesan territory covers civil districts of Karbi Anglong and North Cachar Hills in Assam. Diphu is the biggest city in the diocese. Haflong is the other important town.
In the diocesan area, the population is 1,242,000 in 2016. Karbi, Bodo, Kuki, Dimasa, Hmars, Garo, Rengma Naga, Tiwa, Man, Zeme, Naga, Biates, Hrangkhols, Kehlmas, Adibasi, Pnar, Khasi, Nepali and Bihari are the various ethnic groups in the diocese.
The various languages spoken in the diocesan area are Karbi, Hindi, Assamese, Sadiri, Garo, Tiwa, Bodo, Pnar, Kasi, Kuki, Dimasa and Nepali.
The diocese of Diphu was erected on Dec. 5, 1983, detaching the district of Karbi Anglong from the archdiocese of Shillong-Guwahati and the district of North Cachar Hills from the diocese of Silchar. Father Mathai Kochuparampil SDB was appointed the first bishop of this new diocese. He was installed at Diphu on March 4, 1984. He passed away on March 4, 1992. Father Albano D'Mello was elected diocesan administrator on March 11, 1992. On June 24, 1994, Father John Thomas Kattrukudiyil was appointed the second bishop of the diocese. He was consecrated on Sept. 8, 1994. He was transferred to the newly formed diocese of Itanagar in December 2005. However, he was appointed as the apostolic administrator of the diocese of Diphu as well. On Feb. 14, 2007, Father John Moolachira was appointed as the third bishop of Diphu diocese. He was consecrated on April 15, 2007. Bishop John Moolachira Appointed as Coadjutor Archbishop of Guwahati on April 9, 2011 and Bishop Paul Mattekatt took the office on Jul. 26, 2013.
The oldest missionary presence in the diocese is that of RNDM sisters (Congregation of the Our Lady of the Missions) at Haflong. The first group of sisters settled down in Haflong in 1911. They started a small boarding school, which later was opened to the children of the British engineers and tea garden managers. But due to malaria and other fatal diseases prevalent in the region, the infant school was closed down.
Currently, the diocese has 19 parishes and 23 subcentres. The missionary team of the diocese is made up of the diocesan priests, the Salesians, the MSFS, the Jesuits, Dominicans, OCDs, the Franciscan Brothers, Religious women belonging to 18 different congregations.
Cities are managed by corporations. The villages and small towns are administered by elected local bodies called panchayats and municipalities.
The diocesan area is well connected in terms of transport infrastructure by roads and railway. The nearest airport is in Guwahati.
The per capita income in the diocese's territory is Rs 14,523 ($312) as of November 2009. Rice and Maize are also grown in the area. Major industries include cement production, tea, handloom and textiles, livestock and poultry.
Government and private operators provide extensive telecommunication facilities in the diocesan area. The diocese is well connected by local cable TV networks.
Nearly 62.71 percent is the literacy rate in the diocesan territory.