The freedom struggle of 1857-1858 was followed by the transfer of power from the East India Company to the British Crown. As soon as order had been restored, the civil administration was re-established in the district which was named district Unnao, with headquarters at Unnao. The size of the district was however small till 1869, when it assumed its present form. The same year the town of Unnao was constituted a Municipality.

In ancient times the area covered by the present district of Unnao formed part of the region known as Kosala and was later included in the Subha of Awadh or simply Awadh. This tract appears to have seen civilized and settled life since very early times. Finds from and traces of ancient remains at several places in the district are however, fairly interesting and testify to the antiquity of those sites.

Hiuen Tsang, the famous chinese pilgrim to India, stayed at Kannauj for 3 months in 636 AD. From here he journeyed a distance of about 26 kms and reached the city of Na-fo-ti-po-ku-lo (Navadevakula) which stood on the eastern bank of Ganga. The city was about 5 km in circumference and had in or about it, a magnificent Deva Temple, several Buddhist Monasteries and Stupas. This place, which is about 3 kms north-west of Bangarmau in Tehsil Safipur, has been identified by some scholars with Nawal and is supposed to represent the site of an important ancient city, believed to have been upturned in the 13th century by the curse of a saint, and still called Aundha Khera or Lauta Shahr both meaning an upturned city. The dargah of the Muslim sant, whose curse is said to have befallen the city, is not only the oldest Muslim monument at Bangarmau but perhaps, in the entire district.

By far the most important ancient site in the district is perhaps Sanchankot, also known as Sujankot, which lies in village Ramkot, in pargana Bangarmau of Tehsil Safipur about 55 km north-west of Unnao.

In the days of Akbar, the tract covered by the district was included in sirkar Lucknow of the province of Avadh, and the mahals of his time appear generally speaking, to have been close predecessors of the parganas of today.
During the days of nawabs of Avadh, the eastern portion of the district formed the chakla of Purwa. The portion of the district lying to the north of this chakla were included in the chaklas of Rasulabad and Safipur which also included the mahal of Mohan. Pargana Auras belonged to the chakla of Sandila belonging to district Hardoi. The tract comprised in Pargana Patan, Panhan, Bihar, Bhagwantnagar, Magaryar, Ghatampur and Daundia Khera formed part of the chakla of Baiswara.
After the annexation of Awadh by the British in February 1856, the district, then called district Purwa came into existence and the headquarter was shifted from Purwa to Unnao. The district then contained 13 parganas namely Bangarmau, Fatehpur Chaurasi, Safipur, Pariar, Sikandarpur, Unnao, Harha, Asiwan-Rasulabad, Jhalotar-Ajgain,Gorinda Parsandan, Purwa, Asoha and Mauranwan. In 1869, parganas Panhan Patan, Bihar, Bhagwantnagar, Magaryar, Ghatampur and Daundia khera were transferred from district Rae Bareli to tehsil Purwa of this district, and pargana Auras-Mohan was transferred from district Lucknow to the old tehsil Nawabganj of this district . Whence the tehsil headquarters were removed first to Mohan and, again in 1891, to Hasanganj.