Tirunelveli District is a district of Tamil Nadu state in southern India. The city of Tirunelveli is the district headquarters. Tirunelveli District was formed on 1 September 1790 by the East India Company (on behalf of the British government), and comprised the present Tirunelveli and Thoothukudi districts and parts of Virudhunagar and Ramanathapuram districts. It is the second-largest district (as of October 2008), after Villupuram district. As of 2011, the district had a population of 3,077,233.

Under the rule of the Pandyan Dynasty, the district was known as Thenpandiyanadu. The Chola dynasty then named it Mudikonda Cholamandalam. The Madurai Nayaks called it Tirunelveli Seemai. Under the British East India Company, it was Tinnevelly district, which included the modern Tirunelveli and Thoothukudi districts and parts of the Virudhunagar and Ramanathapuram districts.

In 1910, Ramanathapuram District was formed from portions of the Madurai and Tirunelveli Districts, which comprised portions of the modern Virudhunagar District.After the Independence of India, Tirunelveli District was bifurcated on 20 October 1986 to Nellai-Kattabomman district (Tirunelveli) and Chidambaranar district (Tuticorin). Subsequently, the Government of Tamil Nadu decided to name each district according to the name of the headquarters town, so the region’s name changed from Tirunelveli-Kattabomman to Tirunelveli.

The district is located in the southern part of Tamil Nadu. It borders Virudhunagar District to the north, Thiruvananthapuram, Kollam and Pathanamthitta districts of Kerala to the west, Kanyakumari District to the south and Thoothukudi District to the east. The district covers an area of 6,823 km2. It lies between 8°05′ and 9°30′ north latitude and 77°05′ and 78°25′ east longitude.

The district contains mountains (a stretch of the Western Ghats) and lowland plains, including sandy soil and fertile alluvium, and a variety of flora, fauna and protected wildlife. The district also has inland and mountainous forests. Tirunelveli is said to be the only district of Tamil Nadu to have all the five types of ecological zones as described in the ancient Tamil Literature Kurunji (hilly), Mullai (Forest), Marutham (Flat fertile land), Neithal ( area forming the seashore) and Palai ( Dry desert lands)

Tirunelveli has rainfall in all seasons (953.1 mm in 2005 and 2006), and benefits from both the northeast and southwest monsoons. Most precipitation came from the northeast monsoon (548.7 mm) followed by the southwest monsoon (147.8 mm) and summer rains (184.2 mm). The district is irrigated by several rivers originating in the Western Ghats, such as the Pachaiyar River, which flows into the perennial Tambaraparani River. The Tambaraparani and Manimuthar Rivers have many dams, with reservoirs providing water for irrigation and power generation. The Tamiraparani River provides consistent irrigation to a large agricultural area.The Chittar River also originates in this district. The Courtallam and Manimuthar waterfalls are the two major falls in the district.

According to 2011 census, Tirunelvei district had a population of 3,077,233 with a sex-ratio of 1,023 females for every 1,000 males, much above the national average of 929.A total of 321,687 were under the age of six, constituting 164,157 males and 157,530 females. Scheduled Castes and Scheduled Tribes accounted for 18.51% and .33% of the population respectively. The average literacy of the district was 73.88%, compared to the national average of 72.99%.The district had a total of 815,528 households. There were a total of 1,436,454 workers, comprising 107,943 cultivators, 321,083 main agricultural labourers, 215,667 in house hold industries, 626,714 other workers, 165,047 marginal workers, 7,772 marginal cultivators, 58,680 marginal agricultural labourers, 23,997 marginal workers in household industries and 74,598 other marginal workers.

The district is well-connected by a network of roads and railways. Tirunelveli city serves as the main junction. It has no airports; the nearest airports are at Tuticorin (40 km away), Madurai (150 km) and Thiruvananthapuram (158 km). The district has a total of 27 railway stations. The tables below list the lengths of roads and railways in the district.

Canals, wells, tanks and reservoirs are the sources of irrigation in the district. As of 2005–2006, the district had a total of 151 canals with a length of 499 km, 85,701 irrigation wells, 640 tube wells, eight reservoirs and 2,212 tanks. The district also has 21,776 wells used for domestic purposes.Electricity is provided by the Tamil Nadu Electricity Board (TNEB).The district has hydroelectric power plants and windmills, with an installed capacity of 1,089.675 MW; it is one of the major producers of wind energy in the state.

The Koodankulam Nuclear Power Plant project is being undertaken (with Russian aid) at the village of Koodankulam, 24 km north-east of Kanyakumari, 36 km from Nagercoil and about 106 km from Thiruvananthapuram . Koodankulam is also the location of hundreds of windmills used for power generation, eight of which are located inside the grounds of the nuclear plant. These wind turbines have currently a total capacity of 2000 MW and represent one of the largest wind farms in India. Since the beginning of 2011, this place has been embroiled in a nuclear plant controversy over fears of the plant safety.