Dudhwa Tiger Reserve has two core areas, Dudhwa National Park and Kishanpur Wildlife Sanctuary. These are 15 km apart, with agricultural land in between. Dudhwa National Park is situated on the Indo-Nepal border in the Lakhimpur-Kheri district in Uttar Pradesh. The Mohana river flowing along the Indo-Nepal border constitutes the northern boundary of the Park whilst the Southern boundary is formed by the river Suheli. The Kishanpur Sanctuary lies in the Lakhimpur-Kheri and Shahajahanpur districts in Uttar Pradesh.

The area of the Park is a vast alluvial plain, the doab of the Mohana and Suheli rivers, and interspersed with numerous rivulets, lakes and pools. The rich and extremely fertile Indo-Gangetic plains support a luxuriant growth of forests diversity of fauna.

Some of the grasslands are infested with the weed, Cymbopogon martinii. Dense mats of Tiliacora sq. another weed, has developed in a large portions of the Sal forests. These weeds are inedible and are spreading rapidly, making the affected areas inhospitable for herbivores.
The visit of Sir D.B. Brandis in 1860 to the area culminated in 303 sq. mile forest area of the present day Dudhwa National Park being brought under the control of Government in 1861 for preservation. In Kheri District all the Sal and miscellaneous forests and grasslands in Kharigarh Pargana, between the Mohana and Suheli rivers, were included in the then North Kheri Forest Division. More areas were reserved for protection between 1867 and 1879 and added to the Division. The area of the Division was legally constituted as Reserved Forests in 1937.

The Sonaripur Sanctuary comprising 15.7 sq. km. area was created in 1958 to specifically protect swamp deer (Cervus duvaceli duvaceli). The area was too small and was later enlarged to 212 sq. km. and renamed as Dudhwa Sanctuary in 1968. Later, more area was added to the Sanctuary and in 1977, it was declared Dudhwa National Park. The total area of the Park was 616 sq. km. of which 490 sq. km. was core zone and balance 124 sq. km. buffer zone.

Dudhwa Tiger Reserve was created in the year 1987-88 comprising Dudhwa National Park and Kishanpur Sanctuary (203.41 sq. km.). With an addition of 66 sq. km. to the buffer zone in 1997, the present area of the Tiger Reserve is 884 sq. km.