In 1948, with the formation of PEPSU Mahendragarh territory from Patiala State, Dadri territory (Now Charkhi Dadri) from Jind and Bawal territory from Nabha State were constituted into Mahendragarh district with the headquarters at Narnaul. At that time, there were three tahsils, namely; Narnaul, Charkhi Dadri and Bawal and Mahendragarh was a sub-tahsil. In 1949, Mahendragarh sub-tahsil was made a tahsil. In 1950, Bawal tahsil was broken up and 78 villages were transferred to Gurgaon district forming Bawal as a sub-tahsil and remaining villages were added to Narnaul and Mahendragarh.

In 1956 the Rewari tahsil (except 61 villages ) was excluded from Gurgaon district and included in Mahendragarh district. The Charkhi-Dadri sub- division was excluded from Mahendragarh district and included in the newly constituted district of Bhiwani. In 1977, 81 villages of Rewari tahsil was constituted into Bawal tahsil. In 1978 the district comprised 4 tahsils (Mahendragarh, Rewari, Narnaul and Bawal).

Rewari and Bawal tahsils (taken from Mahendragarh district) and Kosli tahsil except 10 villages (taken from Rohtak district) were constituted into a new district of Rewari as on 1st November, 1989. During this re-organization, Kosli was made a sub-divisional headquarters. By the beginning of 1991, the district had 2 sub-divisions (Narnaul and Mahendragarh)and two tahsils (Mahendragarh and Narnaul).