Chennai district, also and formerly known as Madras district or “Madarasapattinam”, is a district in the state of Tamil Nadu, in India. It is the smallest of all the districts in the state, but has the highest human density. The district is a city district which means that it does not have a district headquarters. Most of the city region of Chennai comes under this district. As of 2011, the district had a population of 4,646,732 with a sex-ratio of 989 females for every 1,000 males.

Chennai district covers an area of 178.2 km2 located on the Eastern Coastal Plains of India. It is situated on the northeastern corner of Tamil Nadu along the Coramandel coast, a region bounded by the Bay of Bengal and is surrounded inland by the districts of Tiruvallur and Kanchipuram. It lies between 12°59′ and 13°9′ of the northern latitude and 80°12′ and 80°19′ of the eastern longitude at an average altitude of 6 metres above sea level on a ‘sandy shelving breaker swept’ beach. Terrain slope varies from 1:5000 to 1:10,000.The terrain is very flat with contours ranging from 2 m to 10 m above mean sea level with a few isolated hillocks in the southwest beyond the district limits at St. Thomas Mount, Pallavaram and Tambaram.The district runs inland in a rugged semi-circular fashion and its coastline is about 25.60 km (2.5% of the total coastline of Tamil Nadu). Because of its strategic location and economic importance, it is referred to as the “Gateway of South India.” The drainage system includes two rivers, namely, Cooum (flowing in the northern part) and Adyar (flowing in the southern part), a canal (the Buckingham), and a stream (the Otteri Nullah) slicing the district into several islands.

The district falls under Seismic Zone III indicating a moderate risk of earthquake. Geologically the district is divided into three regions, namely, sandy, clayey and hard-rock regions. The soil comprises clay, shale and sandstone.

According to 2011 census, Chennai district had a population of 4,646,732 with a sex-ratio of 989 females for every 1,000 males, much above the national average of 929.A total of 459,324 were under the age of six, constituting 235,519 males and 223,805 females. Scheduled Castes and Scheduled Tribes accounted for 16.78% and .22% of the population respectively. The average literacy of the district was 81.27%, compared to the national average of 72.99%.The district had a total of 154,982 households. There were a total of 1,817,297 workers, comprising 10,210 cultivators, 10,251 main agricultural labourers, 29,143 in house hold industries, 1,569,950 other workers, 197,743 marginal workers, 4,244 marginal cultivators, 3,423 marginal agricultural labourers, 8,202 marginal workers in household industries and 181,874 other marginal workers.