The district is divided into two natural divisions: The hilly areas are constituted by parts of the five taluk's Theni, Bodinayakanur, Periyakulam, Uthamapalayam and Andipatti with thick vegetation and perennial streams from the hills on the western side and Cumbum valley which lies in Uthamapalayam taluk.

Consequent to the bifurcation, one new Revenue Division with headquarters at Uthamapalayam and two new Taluks at Theni and Bodinayakanur were also created with effect from 1 January 1997.

After the Mullai-Periyar merger project, many people from nearby arid regions (Sivakasi, Kovilpatti, Virudhunagar, Sattur and several nearby towns) settled in Cumbum Valley (present day Theni District).

The 2,889 km2 (1,115 sq mi) district lies at the foot of the Western Ghats between 9' 39' and 10' 30' North latitude and between 77' 00' and 78' 30' of East Longitude.

The district is home to Theni, Periyakulam, Bodinayakanur, Cumbum, Uthamapalayam, Kombai, Gudalur, Gandamanur, Chinnamanur, Kuchanur, Andipatti, Rasingapuram, Thevaram, Pottipuram, Ramakrishnapuram, B. Ammapatti, Lakshmipuram, Ambasamudram, Govindanagaram, Mayladumparai, Srirengapuram, Venkadachalapuram, K. Pudupatti, Devadhanapatti, Varusanadu, Odaipatti, Erasakkanayackanur and several other small villages like Gohilapuram, Pathirakalipuram, Sukkangalpatti, Kamarajapuram, Sadaiyalpatti, Meenatchipuram, Melasindalaichery, Hanumanthanpatty, Pallavarayan Patti, Genguvarpatti, Jeyamangalam, Thamaraikulam, Kallipatti, Devathanapatti and Kamatchipuram.

A range of hills which runs parallel to Western Ghats from north to south separate it from the neighboring state of Kerala.

[6]: 29  The principal crop production (in tonnes) in 2005-2006 were sugarcane 1,201,221, cotton 95,360 (561 bales of 170. kg lint each), rice (paddy) 66,093, millets and other cereals 57,081, pulses 6,677, groundnut 4,021 and gingelly 325.

[12] Silk, Banana, Coconut, Tea, Coffee, Cardamom, Grapes and Mangoes are other main produce of the district.

Kolukkumalai located in Theni district atop the Western ghats is the home to the highest tea plantation in the world.

Bodinayakanur is a major market place (Auction Centres) for cardamom, coffee, tea and black pepper.

[6]: 15  Theni is one of the active business hubs in the western side of Tamil Nadu, inviting more industries to its locality.

Wattle, softwood, fuel wood, cashew, neem, and tamarind are the main forest plantation species in the district.

[6] According to 2011 census, Theni district had a population of 1,245,899 with a sex-ratio of 991 females for every 1,000 males, much above the national average of 929.

Cascades, silver-lined clouds resting atop green hill tops, sheer rock faces and temples of antiquity distinguish these places.

It has numerous green lands like the Western Ghats stretching from Kodaikanal to Kumily via Periyakulam.

The titles of some of the famous Movies are: "Pithamagan", "Avan-ivan", "Sundarapandiyan", "Veeralaksumi", "Varuthapadatha Vaalibar Sangam", "Naan kadavul".