For the first time, Bengal was partitioned on July 20, 1905.
When Bengal was partitioned, the British official had issued a notification dividing the province of Bengal into two parts: Eastern Bengal and Assam.
Bengal and Assam with a population of 31 million, and the rest of Bengal with a population of 54 millions, of whom 18 million were Bengalis and 36 million Biharis and Oriyas.
The British official put their reason for partitioning Bengal was that the existing Bengal was too big to be efficiently administered by a single provincial government.