The diocese of Buxar is in this state of Bihar. It is comprising of the 4 districts of Buxar, Bhojpur, Bhabua and Rohtas and bifurcated from the western part of Patna Archdiocese, has an area of 11,311 sq. kms., with 15,745 Catholics, 13 parishes/mission stations, 8 diocesan priests, 14 religious priests, 9 religious brothers and 63 religious sisters. The parish church of Buxar is the Cathedral of the new diocese and 'Mary Mother of Perpetual Help', the diocesan Patron.

The announcement of the creation of the diocese was made on Monday, 12th December 2005 at noon local time in Rome, corresponding to 16.30 hours in India.

The first bishop of Buxar, bishop-elect William D'Souza, a Jesuit of the Province of Patna, was born in 1946, ordained priest in 1976 after completing Philosophy in Shembanagur in Tamil Nadu and theology in Jnana Deepa Vidyapeet in Pune.

During his rich and fruitful priestly ministry he was assistant Novice Master, superior of Jesuit communities in various places, Rector of the Minor Seminary in Muzaffarpur, parish priest in several parishes, secretary to the Bishop of Muzaffarpur and Provincial of the Patna Jesuit Province. He was also the Administrator of Muzaffarpur diocese for a year. He was the parish priest of Itarhi in the district of Buxar at the time of his appointment as bishop.