In a land area of 52,283 square kilometers, the diocesan territory covers the ten civil districts of Western Arunachal Pradesh.
Itanagar is the biggest town in the diocese.
Arunachal Pradesh is situated in the North-east corner of India. It is called 'the land of the rising sun' and is the habitat of 26 Mongoloid tribes and their sub tribes scattered over an area of 87,400 square kilometers. This land borders China, Tibet, Bhutan and Myanmar and comprises of snow capped mountains of the Himalayas and flooding river valleys.
In Itanagar diocese, the population is 12,628,834 at end of 2008. (The population of the whole country is 1.2 billion). Adi, Aka, Apatani, Hill Miri, Monpa, Nyishi are the major ethnic groups.
Hindi is widely spoken. Adi, Aka, Apatani, Hill Miri, Monpa, Nyishi are the languages used in the diocesan territory.
The Catholic Church in Itanagar has a unique history. The Indian Government, unhappy with the spread of Christianity among the hill tribes of North-east, decided to keep the Church out of Arunachal Pradesh. The need of an inner line permit for an outsider to enter Arunachal Pradesh helped the government to implement their plan. However, young people from Arunachal who went out of the state seeking good education came into contact with Catholic schools in Assam and Meghalaya. Father L. Cerato SDB, the Parish Priest of N. Lakhimpur accepted several Apatani boys in his school in the early 1960s. He sent some students also to Dibrugarh as N. Lakhimpur was at that time under Dibrugarh Diocese. Bishop Orestes Marengo, the ordinary of Dibrugarh encouraged this apostolate. The first baptisms of Apatanis took place in Lakhimpur in 1963. With the erection of the Diocese of Tezpur in 1964, the Catholic Church was able to give more attention to West Arunachal.Bishop Orestes Marengo, now transferred to Tezpur, used to get enquiries from the government asking whether he was keeping Arunachal students in his schools. In 1969 Father Joseph Mittathany became the Bishop of Tezpur. He began to encourage in a big way admission of Apatani students into various hostels of the diocese. He gave much financial support to this venture. Several students found their way also to other Catholic Institutions in the region especially Shillong and Dibrugarh. Most of these students were baptized and sent back with the mission to evangelize Arunachal Pradesh.
A more significant breakthrough in Arunachal Apostolate came with the establishment of the Parish of Harmuty by Bishop Joseph Mittathany in 1977. The parish is located close to Banderdewa, the entry point to Itanagar, the capital of Arunachal Pradesh. Father Kulandaisamy, a charismatic missionary, was appointed the Parish Priest of Harmuty. It did not take very long before he befriended the Nyishis coming to the Harmuty market. He invited them to the Parish and gave them hospitality. His friendliness and welcome attitude brought him many guests from Arunachal. He baptized some of them. Those baptized were given the mission of bringing others to Harmuty.
Gradually there was a continuous flow of Nyishis to Harmuty Parish. Most of them were baptized before they returned home. In this way several communities came up in the Nyishi belt. Father Kulandaisamy also found various ways to enter Arunachal. He visited many villages and founded communities. He was always a step ahead of the police who were searching for him. He organized for the new Catholics Bible Camps at various places like Harmuty, Doolahat, Tezpur and Shillong. He recruited from among them promising persons and appointed them catechists. Father Kulandaisamy took special interest to place boys and girls in various educational institutions all over North-east. Soon Nyishi students were seen practically in every Catholic boarding in the region. Don Bosco Shillong, where the present Archbishop of Guwahati, Thomas Menamparampil, was the Rector, willingly accepted many students. These students were baptized and motivated to return to their home land as missionaries. The archbishop also did much through his writings, talks and visits to focus the attention of the regional and national Church on Arunachal. From end of 1979, Father Kulandaisamy got the help of a young Salesian Jose Chemparathy to help him in all his works. From 1981 Father Jose joined him as Assistant Parish Priest.
In 1981 Father Robert Kerketta became the Bishop of Tezpur. He continued to intensify the Arunachal Apostolate. In the following year in the month of June a young and zealous Benedictine Brother looking for a mission field to preach the Gospel came to help Father Kulandaisamy. That was Brother Prem Bhai. His missionary spirit took him beyond all borders into every village in West Arunachal Pradesh. His ability to befriend strangers made him a welcome guest everywhere. It would not be an exaggeration to say that his footprints are there in every village in Itanagar Diocese.
The first resident Religious of West Arunachal were the Sisters of the Missionaries of Christ Jesus. They went to live in Ziro as teachers in 1992. In the same year the Missionaries of Charity came to reside in Itanagar. Since they are internationally recognized social workers, the government could not easily deny them Inner Line Permit without attracting adverse attention. Mr. Tok Buttom, a local Catholic leader, helped the sisters find a residence.
Close on the heels of the sisters Father Jose Chemaparathy also moved to Itanagar and the Parish of Itanagar was erected. Open hostility to missionaries gave way to tolerance and then to acceptance. Father Jose built up good rapport with the Government that facilitated the shift in attitude. The Church took advantage of the changed climate and opened a number of Parishes and institutions. More Priests and religious personnel entered Arunachal. The opening of Don Bosco School and Don Bosco College at Jully is an important milestone in the history of the Church in Itanagar Diocese. Very soon the Sisters of the Holy Cross of Chavanod, Salesian sisters, Missionary Sisters of Mary Help Christians and the Franciscan Brothers came to staff institutions stretching from Banderdewa to Itanagar. Brother Prem Bhai opened the Trinity Ashram at Banderdewa in 2002 to facilitate the catechesis of the people. The parish of Naharlugun was erected in 2004 with Father Jacob Mattathilany as Parish Priest.
By this time some of the local young Catholics began to be active in the political scene. Dynamic young persons like Wanglet Lowangsha, Tadar Taniang and Sanjoy Takam fought the elections in 1995 and won their seats in the legislative assembly and also in the cabinet. Their influence helped to create a better climate for the missionaries in Arunachal.
The Christian Brothers from Shillong came to do some pioneering mission work at Sagalee under the leadership of Brother Avinash. They had to abandon the place soon because of a flash flood that washed away their house. Then they moved to Sangram in 1999 where they have now put up one of the best attended rural schools of the diocese. The Missionary Sisters of Mary help of Christians also joined them to help in their educational and medical Apostolate.
The installation of the first Bishop of Itanagar on March 12, 2006 was a joyful event for West Arunachal. The Catholics celebrated the occasion with a sense of triumph; especially those who had gone through hard times because of the earlier antagonism of the government to the Church. The fact that Mr. Nabam Tuki, the PWD minister and a Catholic, was the chairman of the organizing committee facilitated the celebrations. The presence of the Chief Minister along with several cabinet Ministers at the event was an indication that the government had given up on its hard line towards the Church.
The big towns are managed by Corporation. The villages and small towns are administered by elected local bodies called Panchayats and municipalities respectively.
The nearest airport is in Itanagar city.
India Rupees 25, 836 (as of January 2010 USD563) is the per capita income in the diocesan territory. Farming especially agriculture is done by 90 percent of the population, known as Jhum (Shifting cultivation). Petroleum and Coal Mining industries are also situated in the diocese. The state of Arunachal Pradesh has a big potential for hydro electricity power generation.
Government and private operators provide extensive telecommunication facilities in the diocesan area. The diocese is well connected by local cable TV networks.
55 percent is the literacy rate in the area of the diocese.