Purnia has an area of 3,202 square km. It is a level, depressed tract of country, consisting for the most part of a rich, loamy soil of alluvial formation. It is traversed by several rivers flowing from the Himalayas, which afford great advantages of irrigation and water-carriage. Its major rivers are the Kosi, the Mahananda, the Suwara Kali and the Koli. In the west the soil is thickly covered with sand deposited by changes in the course of the Kosi. Among other rivers are the Mahananda and the Panar. Its major agricultural products are jute and banana.
It has a total population of 2,543,942 of which 1,720,743 are rural and 158,142 urban. It had 1,185,356 electors in the 2005. The literacy Rate is 35.10% Purnia district has four subdivisions: Purnea , Baisee , Banmankhi and Dhumdaha and they are further composed of fourteen blocks namely East Purnea,Krityanand Nagar, Banmankhi, Kaswa, Amaur, Bainsi, Baisa, Dhamdaha, Barhara Kothi, Rupauli, Bhawanipur, Dagarua, Jalalgarh and Srinagar.
Purnea has a rich Hindu history and a glorious past.During Mughal rule Purnea was an outlying military province, its revenue was mostly spent on protecting its borders against tribes from the north and east. Its local governor raised a rebellion against Siraj ud-Daulah in 1757, after the capture of Calcutta. In 1765, along with the rest of Bengal, the district became a British possession. Purnea is famous for its uniquely designed Ramakrishna Mission where Durga Puja in the month of April is celebrated with due devotion and honour. Purnea is also famous for the oldest temple of Mata Puran Devi, which is hardly 5 km away from the main city. There is a theory that Purnia got its name from that temple. Some people believe that many years ago Purnea was Purna–Aranya which stands for “complete jungle”, and that’s why it has got the name Purnea.