In 1997, Kausambi was carved out of Allahabad district by the Uttar Pradesh Government as a populist ploy to appeal to its large neo-Buddhist population. Kausambi has a population of 1,293,154 which is 0.78 percent of the population of Uttar Pradesh. It is a predominantly rural district with only 7.10 percent of residents that are urbanized. The three largest towns are Sarai Aquil, Bharwari and Ajhuwa. Scheduled castes and scheduled tribes form 36.11 percent of the population. The three largest scheduled caste groups are Pasi , Chamar and Dhobi. The three largest scheduled tribe groups are Tharu, Generic Tribes and All Scheduled Tribes. 49.96 percent of the district’s population is in the age group of 15-59 years and 6.89 percent is over 59 years.

Kausami has a low overall literacy rate of 46.88 percent and 35.6 percent of girls marry before the legal age of 18 years. (Ref: Census of India, 2001)

Kosambi was one of the greatest cities in India from the late Vedic period till the end of Maurya empire with occupation continuing till the Gupta empire. As a small town, it was established in the late Vedic period.. During the Sunga period, it was the capital of the Vatsa which was a vassal state of the Sungas. After the decline of the Sungas, Vatsa (Kausambi is itself the fomal name associated with recovered coinage) became an independent kingdom (also: Vamsas), one of the Mahajanapadas (Great Kingdoms) of ancient India. Kausambi was a very prosperous city by the time of Buddha, where a large number of wealthy merchants resided. It was an important entreport of goods and passengers from north-west and south. It figures very prominently in the accounts of the life of Buddha. The excavations of the archaeological site of Kausambi was done by the late Prof. G.R.Sharma of the Allahabad University in 1949 and again in 1951-1956 after it was authorized by Sir. Mortimer on March, 1948. Carbon dating of charcoal and Northern Black Polished Ware have historically dated its continued occupation from 390 BC to 600 A.D. .

Kosambi was a fortified town with an irregular oblong plan. Excavations of the ruins revealed the existence of gates on three sides-east, west and north. The location of the southern gate can not be precisely determined due to water erosion. Besides the bastions, gates and sub-gates, the city was encircled on three sides by a moat, which, though filed up at places, it still discernible on the northern side. At some points, however, there is evidence of more than one moat. The city extended to an area of approximately 6.5 KM. The city shows a large extent of brickworks indicating the density of structures in the city.

The Buddhist Commentarial scriptures give two reasons for the name Kausambi/Kosambī. The more favoured is that the city was so called because it was founded in or near the site of the hermitage once occupied by the sage Kusumba (v.l. Kusumbha). Another explanation is that large and stately margosa-trees (Kosammarukkhā) grew in great numbers in and around the city.

In the time of the Buddha its king was Parantapa, and after him reigned his son Udena(Pali. Udayana in Sanskrit) . Kosambī was evidently a city of great importance at the time of the Buddha for we find Ananda mentioning it as one of the places suitable for the Buddha's Parinibbāna . It was also the most important halt for traffic coming to Kosala and Magadha from the south and the west.

The city was thirty leagues by river from Banares(modern day Varanasi). (Thus we are told that the fish which swallowed Bakkula travelled thirty leagues through the Yamunā, from Kosambī to Banares). The usual route from Rājagaha to Kosambī was up the river (this was the route taken by Ananda when he went with five hundred others to inflict the higher punishment on Channa, Vin.ii.290), though there seems to have been a land route passing through Anupiya and Kosambī to Rājagaha). In the Sutta Nipāta (vv.1010-13) the whole route is given from Mahissati to Rājagaha, passing through Kosambī, the halting-places mentioned being: Ujjeni, Gonaddha, Vedisa, Vanasavhya, Kosambī, Sāketa, Sravasthi/Sāvatthi, Setavyā, Kapilavasthu/Kapilavatthu, Kusinārā, Pāvā, Bhoganagara and Vesāli.

Near Kosambī, by the river, was Udayana/Udena's park, the Udakavana, where Ananda and Pindola Bharadvaja preached to the women of Udena's palace on two different occasions. The Buddha is mentioned as having once stayed in the Simsapāvana in Kosambī. Mahā Kaccāna lived in a woodland near Kosambī after the holding of the First Buddhist Council.

Already in the Buddha's time there were four establishments of the Order in Kosambī - the Kukkutārāma, the Ghositārāma, the Pāvārika-ambavana (these being given by three of the most eminent citizens of Kosambī, named respectively, Kukkuta, Ghosita and Pāvārika), and the Badarikārāma. The Buddha visited Kosambī on several occasions, stopping at one or other of these residences, and several discourses delivered during these visits are recorded in the books. (Thomas, op. cit., 115, n.2, doubts the authenticity of the stories connected with the Buddha's visits to Kosambī, holding that these stories are of later invention).

The Buddha spent his ninth rainy season at Kosambī, and it was on his way there on this occasion that he made a detour to Kammāssadamma and was offered in marriage Māgandiyā, daughter of the brahmin Māgandiya. The circumstances are narrated in connection with the Māgandiya Sutta. Māgandiyā took the Buddha's refusal as an insult to herself, and, after her marriage to King Udena (of Kosambi), tried in various ways to take revenge on the Buddha, and also on Udena's wife Sāmavatī, who had been the Buddha's follower.