The Nilgiris district (நீலகிரி மாவட்டம்) is one of the 38 districts in the southern Indian state of Tamil Nadu. Nilgiri (Blue Mountains) is the name given to a range of mountains spread across the borders among the states of Tamil Nadu, Karnataka and Kerala. The Nilgiri Hills are part of a larger mountain chain known as the Western Ghats. Their highest point is the mountain of Doddabetta, height 2,637 m. The district is contained mainly within the Nilgiri Mountains range. The administrative headquarters is located at Ooty (Ootacamud or Udhagamandalam). The district is bounded byCoimbatore to the south, Erode to the east, and Chamarajnagar district of Karnataka and Wayanad district of Kerala to the north. As it is located at the junction of three states, namely, Tamil Nadu, Kerala, and Karnataka, significant Malayali and Kannadiga populations reside in the district. Nilgiris district is known for natural mines of Gold, which is also seen in the other parts of Nilgiri Biosphere Reserve extended in the neighbouring states of Karnataka and Kerala too.
Nilgiris district ranked first in a comprehensive Economic Environment index ranking districts in Tamil Nadu (except Chennai district) prepared by the Institute for Financial Management and Research in August 2009. Tea and coffee plantations have been important to its economy. As of 2011, the Nilgiris district had a population of 735,394, with a sex-ratio of 1,042 females for every 1,000 males. All types of single use plastics are banned in Nilgiris district: it is the first plastic free district in Tamil Nadu.
The history of peoples settled in the Nilgiri hills has been recorded for several centuries. The Blue Mountains were likely named for the widespread blue Strobilanthes flower or the smoky haze enveloping the area.
This area was long occupied by the indigenous tribal peoples of the Toda, Kota, Kurumba, Irula and Badagas. The Badagas were also indigenous to the district but were never a tribal group. Particularly Vulnerable Tribal Groups PVTGs, the dominant land owners of the tribal district.