In a land area of 62,103 square kilometers, the diocesan territory covers three districts in West Kalimantan province: Sintang, Kapuas Hulu and Melawi.
Sintang district with 21,638 square kilometers has 17 subdistricts: Ambalau, Binjai Hulu, Dedai, Kayan Hilir, Kayan Hulu, Kelam Permai, Ketungau Hilir, Ketungau Hulu, Ketungau Tengah, Sei Tebelian, Sepauk, Serawai, Sintang and Tempunak.
Kapuas Hulu with 29,824 square kilometers has 23 subdistricts: Badau, Batang Lupar, Batu Datu, Boyan Tanjung, Bunut Hilir, Bunut Hulu, Embaloh Hilir, Embaloh Hulu, Embau, Empanang, Hulu Gurung, Kalis, Putussibau Selatan, Bika, Mentebah, Puring Kencana, Putussibau Utara, Seberuang, Selimbau, Semitau, Silat Hilir, Silat Hulu, Suhaid.
Melawi with 10,641 square kilometers has 11 subdistricts: Belimbing Hulu , Nanga Pinoh, Menukung, Sokan, Sayan, Tanah Pinoh, Belimbing, Pinoh Utara, Pinoh Selatan, Tanah Pinoh Barat.
The transportation that links all towns in these three districts are river, road and path.
As of 2017, a total of 1,018,483 people lived in the territory. The natives of West Kalimantan are the Dayak people, but now the province has Malay and Chinese people. The government-run transmigration program had brought also Javanese and Florinese people to West Kalimantan.
The Catholic mission in Sintang diocese starts in Sejiram when Apostolic Vicar Monsignor AC Claessens of Batavia informed in his Feb. 25, 1884 letter about his meeting with the Governor General of the Dutch East Indies that gave Borneo to the Catholic mission.
On July 29 1890, Father H. Looymans arrived in Semitau as the first mission for the Dayaks. Due to the fact that only Chinese and Malays stayed in Semitau, in 1892 Father Looymans was brought to Sejiram, where he built a house on the riverside of Seberuang River, surrounded by four Dayak villages.
The priest then built a church, school and a small house for school children. Only in seven months Father Looymans had baptized 58 boys and girls. But Father Looymans and Father Mulder had to leave Sejiram in 1898.
Kalimantan became an apostolic prefecture on Feb. 11, 1905. The first apostolic prefect, based in Pontianak, was Father Pacificus Bos OFMCap. He was appointed on April 10, 1905.
It was in May 1906, when the apostolic prefect visited Sejiram. Based on that visit, on Aug. 22, 1906, Father Pacificus Bos restored the mission station of Sejiram and sent Capuchin missionaries, Father Eugenius, Father Camillus and Brother Theodorius. Some Franciscan sisters followed them. But, they found no church, school and houses constructed earlier by Father Looymans however, the faith of the baptized people was still there.
They build a new church and parish house and launched spiritual activities and social works, including a plantation for the Dayaks' socio-economic development. They also started education even though the priests had to go to the villagers to find pupils.
In 1939, Montfort missionaries replaced the Capuchins. Three Montfort missionaries arrived in Sintang in that year. More mission stations were opened in Sintang, and on March 11, 1948, Sintang with five missions stations became an apostolic prefecture with Monsignor Lambertus van Kessel SMM as its first prefect.
In the same year the first Dayak was ordained a priest, Father Aloysius Ding.
Apostolic prefecture of Sintang improved to become an apostolic vicariate on April 23, 1956. On Jan. 3, 1961, Pope John XXIII established the Catholic hierarchy in Indonesia. Sintang was declared a diocese and Monsignor Lambertus van Kessel SMM became its first bishop. He resigned in August 1973.
Father Isak Doera was appointed bishop of Sintang on Dec. 9, 1976, and ordained bishop on May 19, 1977. He was then assisted by Ursuline sisters and Caritas sisters, and by more catechists graduated from the School for Catechetic founded by Mgr Van Kessel. Bishop Isak Doera resigned on Jan. 1, 1996.
Bishop Agustinus Agus was appointed bishop of Sintang on Oct. 29, 1999. His episcopal ordination was on Feb. 6, 2000.
Sintang and Putussibau have small airports. The land transportations are still poor. Not all villages can be accessed by roads. River transportation is available the diocese.
The main industries in the diocese are rubber, timber and palm oil.
The telecommunication in the diocese is not so good. Not all parts in the diocese can be reached by phone, the Internet, television and radio.
The education in the capitals of the districts is good, but illiteracy is more prevalent in hinterland or rural areas of West Kalimantan due to the limitation of teachers.
Sintang diocese is rich in cultures. The Dayak parishioners in hinterlands still live in Dayak traditional house called "betang" built in many cultures. Dayak has many tribes. Kapuas Hulu district, for example, has 20 tribes of Dayak with different language, tradition and culture, such as traditional dance, music instruments, literature, weaving, handicrafts, cakes, and food.
The dwellers of betang live in tolerance and hospitalities. They cooperate in cultivating fields and cleaning the betang. Tribal law solves the conflicts among “betang” dwellers.