Before 1947

Before 1947, Madras Presidency under British Raj was made up of 26 districts, of which 12 districts were part of the boundaries of the present-day Tamil Nadu, namely, Chingleput, Coimbatore, Nilgiris, North Arcot, Madras, Madura, Ramnad, Salem, South Arcot, Tanjore, Tinnevely, and Trichinopoly.^[1]

1947–56

After Indian Independence, the Madras Presidency] became the Madras Province on 15 August 1947. Pudukottai, a princely state acceded to the Indian Union on 4 March 1948 and became a division in Trichinopoly district.^[2] When the new constitution came into force on 26 January 1950, Madras Province became Madras State. Madras state included most of the present-day Tamil Nadu, Coastal Andhra and Rayalaseema of Andhra Pradesh, the Malabar region of Kerala, Bellary and South Canara districts of Karnataka.^[3] Coastal Andhra and Rayalaseema were separated to form Andhra State in 1953.^[4] As a result of the re-organization of states in 1956, South Canara and Bellary districts were merged with Mysore State to form Karnataka and Malabar district with the State of Travancore-Cochin to form Kerala in 1956.^[5] The Tamil speaking regions of Kanyakumari which was earlier a part of Travancore-Cochin was merged to Madras state.^[5] Madras state had 13 districts namely: Chingleput, Coimbatore, Kanyakumari, Madras, Madurai, Nilgiris, North Arcot, Ramanathapuram, Salem, South Arcot, Thanjavur, Tiruchirappalli and Tirunelveli.^[6]

1957–89

• On 2 October 1965, Dharmapuri district was bifurcated from the erstwhile Salem district comprising Dharmapuri, Harur, Hosur and Krishnagiri taluks.^[7]
• In 1969, Madras State was renamed as Tamil Nadu.^[8]
• On 14 January 1974, Pudukkottai district was formed from the parts of Tiruchirappalli] and Thanjavur districts comprising Kulathur, Thirumayam, Alangudi and Aranthangi taluks.^[2]
• On 31 August 1979, Erode district was bifurcated from the erstwhile Coimbatore district comprising Gobichettipalayam and Erode taluks.^[9]
• On 8 March 1985, Sivaganga and Virudhunagar districts were formed from the erstwhile Ramanathapuram district with Sivaganga comprising Tirupattur, Karaikudi, Devakottai, Sivaganga, Manamadurai and Ilayangudi taluks and Virudhunagar comprising Srivilliputhur, Virudhunagar, Tiruchuli, Aruppukottai, Sattur and Rajapalayam taluks.^[10][11]
• On 15 September 1985, Dindigul district was bifurcated from the erstwhile Madurai district comprising Dindigul, Palani and Kodaikanal taluks.^[12]
• On 20 October 1986, Thoothukudi district was bifurcated from the erstwhile Tirunelveli district comprising Thoothukudi, Ottapidaram and Tiruvaikuntam taluks.^[13]
• On 30 September 1989, Tiruvannamalai and Vellore districts were formed from the erstwhile North Arcot district with Tiruvannamalai district comprising Tiruvannamalai, Arni, Vandavasi, Cheyyar, Polur and Chengam taluks^[14] and Vellore district comprising Arakkonam, Arcot, Gudiyatham, Tirupattur, Vellore, Vaniyambadi and Walajapet taluks.^[15]

1990–99

• On 18 October 1991, Nagapattinam was bifurcated from the erstwhile Thanjavur district comprising Tiruvarur, Mayiladuthurai, Manargudi, Needamangalam, Nagapattinam taluks and Valangaiman from Kumbakonam taluk.^[16]
• On 30 September 1993, Cuddalore and Viluppuram districts were formed from the erstwhile South Arcot district with Cuddalore district comprising Cuddalore, Chidambaram and Vriddachalam taluks and Villupuram district comprising Kallakuruchi, Villupuram, Tirukkoyilur and Tindivanam taluks.^[17][18]
• On 30 September 1995, Karur and Perambalur districts were split from the erstwhile Tiruchirappalli district with Karur district comprising Karur, Kulithalai and Manapparai taluks and Perambalur district comprising Perambalur and Kunnam taluks.^[19][20]
• On 25 July 1996, Theni district was bifurcated from the erstwhile Madurai district comprising Theni, Bodinayakanur, Periyakulam, Uthamapalayam and Andipatti taluks.^[21]
• On 1 January 1997, Tiruvarur district was formed from the parts of erstwhile Nagapattinam and Thanjavur districts comprising Tiruvarur, Nannilam, Kudavasal, Needamangalam, Mannargudi, Thiruthiraipoondi taluks from Nagappatinam district and Valangaiman taluk from Thanjavur district.^[22]
• On 1 January 1997, Namakkal district was bifurcated from the erstwhile Salem district comprising Namakkal, Tiruchengode, Rasipuram and Paramathi-Velur taluks.^[23]
• On 1 July 1997, Kanchipuram and Tiruvallur districts were split from the erstwhile Chengalpattu and Chennai districts with Kanchipuram district comprising Kanchipuram, Sriperumbudur, Uthiramerur, Chengalpattu, Tambaram, Tirukalukundram, Maduranthakam and Cheyyur taluks and Tiruvallur district comprising Tiruvallur, Tiruttani, Ponneri and Gummidipoondi taluks.^[24]

2000–present

• On 9 February 2004, Krishnagiri district was bifurcated from the erstwhile Dharmapuri district comprising Krishnagiri, Hosur, Pochampalli, Uthangarai and Denkanikottai taluks.^[25]
• On 19 November 2007, Ariyalur district was bifurcated from the erstwhile Perambalur district comprising Ariyalur, Udayarpalayam and Sendurai taluks.^[26]
• On 24 October 2009, Tiruppur district was formed from the parts of Coimbatore and Erode districts comprising Tiruppur, Udumalpet, Palladam and parts of Avinashi taluks of Coimbatore district and Dharapuram, Kangeyam and parts of Perundurai taluk of Erode district.^[27]
• On 5 January 2018, the Chennai district was expanded by the addition of Madhavaram, Maduravoyal, Ambattur, Tiruvottriyur taluks and parts of Ponneri taluk of Tiruvallur district and Alandur and Sholinganallur taluks of Kanchipuram district.^[28]
• On 22 November 2019, Tenkasi district was bifurcated from the erstwhile Tirunelveli district comprising Tenkasi, Sengottai, Kadayanallur, Sivagiri, Veerakeralampudur, Sankarankovil, Thiruvenkatam and Alangulam taluks.^[29]
• On 26 November 2019, Kallakurichi district was bifurcated from the erstwhile Viluppuram district comprising Kallakurichi, Sankarapuram, Chinnasalem, Ulundurpet, Thirukovilur and Kalvarayanmalai taluks.^[30]
• On 29 November 2019, Tirupattur and Ranipet districts were trifurcated from the erstwhile Vellore district with Tirupattur district comprising Tirupattur, Vaniyambadi, Natrampalli and Ambur taluks and Ranipet district comprising Walajah, Arcot, Nemili and Arakkonam taluks.^[31]
• On 30 November 2019, Chengalpattu district was bifurcated from the erstwhile Kanchipuram district comprising Tirukalukundram], Chengalpattu, Madurantakam, Cheyyar, Tiruporur, Tambaram, Pallavaram and Vandalur taluks.^[32]
• On 24 March 2020, Mayiladuthurai district was bifurcated from the erstwhile Nagapattinam district comprising Mayiladuthurai, Sirkazhi, Tharangambadi and Kuthalam taluks.^[33]

Active districts

Former districts