Before the reunification of Nepal by Gorkha King Prithivi Narayan Shah, this district was part of the Doti Kingdom.

Nepal lost it to the East India Company after the Anglo-Nepalese war (1814-1816) between the then Kingdom of Nepal and the East India Company followed by territorial concessions under the Sugauli Treaty.

Later on after the treaty of 1860, Nepal recovered this land along with Kanchanpur, Banke and Bardiya.

At the time of the 2011 Nepal census, Kailali District had a population of 775,709.

[3] Caste/ethnicity of Kailali district (2011)[4] Ethnicity/caste: 41.9% were Tharu, 20.8% Chhetri, 12.4% Hill Brahmin, 8.4% Kami, 3.9% Thakuri, 3.8% Magar, 2.2% Damai/Dholi, 1.1% other Dalit, 0.9% Sarki, 0.6% Musalman, 0.5% Lohar, 0.5% Sanyasi/Dasnami, 0.4% Badi, 0.4% Newar, 0.3% Raji, 0.3% Tamang, 0.2% Gurung, 0.2% other Terai, 0.1% Terai Brahmin, 0.1% Halwai, 0.1% Kathabaniyan, 0.1% Rai, 0.1% Yadav and 0.1% others.