After India became free in 1947, there was a demand in some quarters for the merger of Hill States with the east Punjab but it met with vehement opposition from the rulers and people. In what is Himachal Pradesh today, the Praja Mandal workers and the rulers had different opinions about the future of these hilly states. After a brief spell of hectic negotiation, the rulers and the Praja Mandal workers decided to inform Government of India to form a union of these small hill states with the name of Himachal Pradesh. In view of these events, the Central Government decided to integrate all these principalities into a single unit to be administered by Govt. of India through a Chief Commissioner.
As a result, Himachal Pradesh came into being as a part ‘C’ State of the Indian Union on 15th April, 1948 by integration/merger together of 31 big and small hill states.These states were Baghat, Bhajji, Baghal, Bija, Balsen, Bushehar, Chamba, Darkoti, Deloth-Dhadi, Dhami, Ghund, Jubbal, Khaneti, Kyarkoti, Kumarsain, Kunihar, Kuthar, Mandi, Madhan, Mahlog, Mangal, Kot(Ratesh), Keonthal, Rawinigarh, Sangri, Sirmaur, Suket, Tharoch & Theog. All these areas at that time constituted four districts viz. Chamba, Mahasu, Mandi and Sirmaur with an area of 27,169 square kilometres. In 1954, the neighbouring State of Bilaspur was integrated with Himachal Pradesh, thereby adding one more district with an area of 1167 square kilometres.
Himachal Pradesh continued as a part ‘C’ State of the Indian Union till 1956 when the states’ Reorganisation Commission submitted its recommendations to abolish the categorisation of states as part A, B, C, etc. and recommended the merger of all part `C’ states either with the adjoining states of higher status or to maintain these independently as union territories till a further decision was taken. Himachal Pradesh continued to exist as a Union Territory till the conferment of statehood on 25th January 1971 .
In 1960, the border Chini tehsil of Mahasu district was carved out as a separate administrative unit and district Kinnaur was formed raising the total number of districts to six. On Ist November, 1966, the then Punjab State was reorganised with the formation of Haryana as a separate state and merger of the then Kullu, Kangra, Shimla and some hilly areas of Hoshiarpur district and Dalhousie of Gurdaspur district into Himachal Pradesh constituting the four new districts viz. Kullu, Lahaul & Spiti, Kangra and Shimla in Himachal Pradesh and merging Dalhousie into Chamba district. With this addition, Himachal Pradesh comprised of ten districts, an area of 55,673 sq. Kilometres and a population of 28.12 lakh according to 1961 census.
On Ist September 1972, two more districts viz. Hamirpur and Una were created by trifurcation of Kangra district and the Mahasu and Solan districts were reorganised as Shimla and Solan districts. In this re-organisation, Shimla town was re-organised with the erstwhile Mahasu district to form Shimla district.