After India became independent, its constituent units were classified into 4 distinct categories – Part A, Part B, Part C, Part D. Their composition is as follows
Part C states were administered by the President through a Chief Commissioner or Lieutenant-Governor.
1956 : States Reorganization Act. Abolished the above 4-fold classification. Part A and Part B were merged. Part C territories – HP(including Bilaspur), Delhi, Manipur, Tripura were made UTs and the rest of them were merged with their adjoining states. Part D(Andaman & Nicobar Islands) was made a UT. As a result we had 14 States and 6 UT.
1960 : Bilingual state of Bombay was divided into Maharashtra and Gujrat. Gujrat becomes the 15th State.
1961 : Dadra and Nagar Haveli, Portuguese colony till 1954 was converted into a UT by the 10th Constitutional Amendment Act. Dadra and Nagar Haveli becomes the 7th UT.
1962 : Goa, Daman and Diu acquired from Portuguese by means of police action in 1961. Constituted as UT by the 12th Constitutional Amendment Act in 1962. They come 8th and 9th UT respectively.
1962 : State of Nagaland carved out from the state of Assam by 13th Constitutional Amendment Act in 1962. Nagaland becomes the 16th State.
1962 : 4 French establishments – Puducherry, Karaikal, Mahe and Yanam where handed over to India in 1954. Made a UT by the 14th Constitutional Amendment Act in 1962. Puducherry becomes the 10th UT.
1966 : Punjab was bifurcated to create Haryana. UT of Chandigargh was formed. Hilly Areas of Punjab were merged with Himachal Pradesh. Haryana becomes the 17th State. Chandigargh becomes the 11th UT.
1970 : HP elevated from status of UT to the status of state. HP becomes the 18th State. Total UT-count comes down to 10.
1971 : Political Map of NE underwent a major Change. Manipur, Tripura and Meghayala elevated to the status of state. The total State-count becomes 21.
1975 : Referendum held in Sikkim and Sikkim became an integral part of India. 36th Constitutional Amendment made it the 22nd full-fledged state.
1987 : Goa elevated from status of UT to the status of state. Becomes the 25th State. Total UT-count comes down to 7.
1991 : Delhi becomes the National Capital Territory of Delhi.
2014 : Andhra Pradesh bifurcated to form Telangana. Becomes the 29th State.