The territory of the present-day district comprises the territories of the erstwhile princely states of Bhagal, Bhagat, Kunihar, Kuthar, Mangal, Beja, Mahlog, Nalagarh and parts of Keonthal and Kothi and hilly areas of the erstwhile Punjab State which were merged with Himachal Pradesh on 1 November 1966. This district came into existence on 1 September 1972. The district was carved out by amalgamating Solan and Arki tehsils of the erstwhile Mahasu district and Kandaghat and Nalagarh tehsils of the erstwhile Shimla district. Its name comes from Mata Shoolini Devi. It's said that she saved Solan from been destroyed.