Mainpuri district (Hindi pronunciation: [mɛːn̪.pʊɾiː]) is one of the districts in the Agra division of Uttar Pradesh, India. Mainpuri town is the district headquarters. Mainpuri is located in the southwestern part of Uttar Pradesh, within the Agra division. It is situated in the Ganges-Yamuna Doab region. It consists of six tehsils, namely Mainpuri, Bhongaon, Karhal, Kishni, Kurawali and Ghiror.

Mainpuri forms part of the ancient legendary region of Lord Krishna's land called Braj. It is bounded on the north by Etah district, on the east by the districts Farrukhabad and Kannauj, on the south by Etawah district and on the west by the districts Firozabad and Etah. It lies between north latitude 260 53′ to 270 31′ and east longitude 780 27′ to 790 26′. According to the 2011 census, Mainpuri district has a population of 1,847,194. The district has a population density of 670 inhabitants per square kilometre (1,700/sq mi). Mainpuri has a sex ratio of 876 females for every 1000 males, and a literacy rate of 78.26%.

Several copper harpoons and antenna swords have been found in Ganeshpur village in 2022 which are from Copper Hoard Culture. The region was part of Dakshina Panchala, with its capital at Kampilya in the nearby Farrukhabad district. Ruled by the Nandas, Mauryas, Shungas, Kanvas, Kushanas, the Panchala region gained immense prosperity under the Guptas. Not much mention is made of the region until the time of the Maukharis and later Harsha. From this time, the region was ruled by dynasties centred at Kannauj, particularly the Gurjara-Pratiharas. After their fall, a period of brief anarchy followed in the district until the rise of the Gahadavala dynasty in the late 11th century. After Mohammad Ghori defeated Jayachandra, the last king of Kannauj, the region was divided into a number of petty principalities, of which Rapri and Bhongaon were chief. These principalities initially attempted to resist the consolidation of authority under the Sultans of Delhi, but were unsuccessful. Qutubuddin Aibak made Rapri in neighbouring Firozabad district the centre of an iqta tax farming grant, which remained an important centre for centuries to come. Bhongaon was given as fief to Malik Sher Khan, nephew of Balban, in 1259 and was held for one year. Malik Kafur held Rapri as fief under Alauddin Khilji.

In 1392 Bir Bhan, the Muqqadam of Bhongaon, rose in revolt against the Sultan Muhammad Shah Tughluq, which was crushed by the vizier. However the next year he, along with Sarvadharan and Abhai Chand, two other nobles, he rose in revolt again. The revolt was only ended when Mukarrab-ul-Mulk, governor of Jalesar, murdered two of the ringleaders under the pretext of peace talks. Eventually the territory up to Rapri fell under the rule of the Jaunpur Sultanate. During the struggle between Delhi and Jaunpur after the invasion of Timur, the Hindu chiefs of Mainpuri again tried to declare indpenedence and were crushed. In 1420, Taj-ul-Mulk, vizier of Khizr Khan, sacked Mainpuri when suppressing the rebellion of more Hindu chiefs of the district and destroyed their stronghold of Dhiluli.

During the reign of Alauddin Alam Shah, one Rai Pratap of Bhongaon instigated the Sultan to try to execute his vizier, whose father had carried off his wife. The vizier instead offered the crown to Bahlul Lodhi and forced the Sayyid dynasty out of power, although Rai Pratap was still confirmed in his position. The district remained at the frontier of the Delhi and Jaunpur sultans, but was not much mentioned. After Babur's conquest of Delhi and the anarchy that followed his death, the region fell under the Suri Empire, and was reconquered by the Mughals. In 1562, Akbar himself was injured in this district when trying to quell resistance from the people of Paronkha village. During his time, the present area of the district was in Agra Subah, divided between the pargana of Ghiror in Agra sarkar, and the mahals of Bhongaon, Patti Alipur, Sauj, Tais, part of Etawah, and Kuraoli, most of which was controlled by Rajputs. The region's status remained relatively unchanged until the death of Aurangzeb in 1707.

The region then fell under the control of Muhammad Khan Bangash, an Afghan noble who aided Farrukhsiyar become Mughal emperor, and remained under his rule until his death in 1743. Afterwards the Marathas took control of the area, until the Third Battle of Panipat when it ended up part of the Rohilla possessions, before being taken by the Nawab of Awadh. The Marathas retook the region in 1770, but were soon expelled by Awadh and the British in 1774, and the region was ruled by the Nawab until 1801. During the Second Anglo-Maratha War in 1804, Yashwantrao Holkar attacked Mainpuri.

When this part of the country was ceded to the British in 1801, Mainpuri town became the headquarters of the extensive district of Etawah, which covered much of the middle Doab with tehsils Shikohabad, Huzur, Sakit, Kasganj and Etawah. Soon after 1803, Sauj pargana was transferred to Farrukhabad, and the tehsils were placed under subcollectorates. In 1827, Kuraoli was transferred from Farrukhabad, as was Bewar in 1840. In 1824 a separate Karhal pargana was created and the Rapri pargana was divided into a Shikohabad pargana and two other parganas: Mustafabad and Ghiror, and the Manchhana pargana was formed out of Bhongaon. In 1837, Mainpuri was separated from Etawah district and in 1845 the Etah district was formed out of the three northern parganas of the district. In 1850 Manchhana taluk was re-merged with Bhongaon. In 1861, Sauj pargana was divided between Karhal and Mainpuri. Small land transfers were made to Farrukhabad, Etawah and Etah districts in 1957, and in 1961 some land was transferred from Farrukhabad district to Mainpuri district.

On the outbreak of the Rebellion in 1857 and receipt of the news of the mutiny of troops in Aligarh, the regiment stationed at Mainpuri revolted and attacked the town in late May, parts of which were defended by the few Europeans of the station and some loyal Indian troops led by Zamindar Rao Bhawani Singh. Mainpuri remained under slowly faltering British control for longer than the surrounding districts until the end of June, when the British authority completely collapsed. The arrival of a force of Jhansi mutineers on June 29 made it necessary to abandon the district to the care of Raja Tej Singh, who claimed to be loyal, and they opened the jail with some of his uncle Bhawani Singh's men who joined the revolt. However Bhawani Singh himself remained loyal, as he benefited from the ealier seizure of his nephew's land by the British. When more revolutionaries from Sagar arrived, the Raja set up his revolutionary administration. Tej Singh suppressed the Ahir zamindars of Bharaul and made alliance with the Nawab of Farrukhabad. In October, the British tried to reconquer the middle Doab but once they left, Tej Singh returned to take over the region by December. However a British force soon beat him near Kuraoli, forcing them to retreat and allowing the British to reoccupy Mainpuri. The district was under full British control again by late 1858.