In a land area of 6,693 square kilometers, the diocesan territory covers the ten taluks of the civil district of Thane in Maharastra state.
Vasai is the biggest town in the diocese. Dahanu, Palghar and Shahapur are other important towns in the diocese.
As of Census 2017, the total population in the diocesan territory is 3,972,940. Marathis form the major ethnic group.
Marathi, Konkani, Kannada, Tamil, Malayalam, Hindi, English and Varli are the languages used in the diocesan territory.
The history of Vasai is as old as Christianity itself. Tradition has it that St. Bartholomeo, the apostle, came to Kalyan which forms part of Thane district in which the diocese of Vasai is situated. In the 6th century, Kalyan had a bishop elected and sent from Persia. Jordenus worked as a Dominican priest for a brief period in a church at Sopara in 1321 in this diocese when he had come just as a father before he was appointed as the first bishop of Quilon.
In 1534, the Portuguese moved to Vasai from Cochin and Goa. In 1536, they put up a church in Vasai Fort dedicated to Our Lady of Life. There was also a parish church under the title of St. Joseph. This church was known as the 'Se' or 'Seat of the Bishop.' Whenever the bishop of Goa visited Vasai that was the church from where he officiated.
With the arrival of the Portuguese Fathers, the Franciscans, Dominicans, Jesuits, Augustinians, they started sending their priests to Vasai. (The Brothers of St. John of God were also among them). They erected three big churches in North Vasai and about five churches in South Vasai. There were churches built by them in Palghar and Dahanu Talukas. Today, they do not exist anymore. The Catholics of the former 8 churches are being served today by the 33 ecclesiastical units which form the major part of this diocese.
The Church in this diocese had its ups and downs during during the Maratha and the British rule, but the priests that came from Goa kept up the faith when the European Fathers were driven away. The local priests coming from the East Indian Community were among the first ones to help the Goan priests in preserving the faith of the people of this area which they had received from the Portuguese from the 16th Century.
The new Diocese of Vasai was created on May 22, 1998, by Pope John Paul II. The installation ceremony of Father Thomas Dabre as the first bishop of the new diocese took place at the new Cathedral of Our Lady of Grace, Papdy, on Aug. 15, 1998. On April 4, 2009, Bishop Dabre was transferred to the diocese of Poona. Archbishop Machado of Nashik diocese was transferred to the diocese of Vasai on Nov. 10, 2009, and was installed on Dec. 19, 2009.
The villages and small towns are administered by elected local bodies called panchayats and municipalities respectively.
The diocesan area is well connected in terms of transport infrastructure by roads and railways. The nearest airport is in Mumbai city, formerly called Bombay.
The per capita income in the diocese territory is Rs 18,723 ($406) as of February 2010. Agriculture and fishing are leading occupation in the area.
Government and private operators provide extensive telecommunication facilities in the diocesan area. The diocese is well connected by local cable TV networks.
Nearly 80.66 percent is the literacy rate in the diocesan territory.