The city of Mahendragarh was formerly known as Kanoud because of Kanauadia populated by Brahmins. It is said that Malik Mahadud Khan, a servant of Babar had settled. In the seventeenth century, Maratha ruler Tanti Tope built a fort here. In 1861, ruler Maharaja Narendra Singh of Patiala principality had named this fort in Mahendergarh in honor of his son Mohinder Singh. Because of the name of the fort, this town came to be known as Mahendragarh and the name of Narnaul Nizam was changed to Mahendragarh Nizam.
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 tehsils, namely; Narnaul, Charkhi Dadri and Bawal and Mahendragarh was a sub-tehsil. In 1949, Mahendragarh sub-tehsil was made a tehsil. In 1950, Bawal tehsil was broken up and 78 villages were transferred to Gurgaon district forming Bawal as a sub-tehsil and remaining villages were added to Narnaul and Mahendragarh.
In 1956 the Rewari tehsil (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 tehsil was constituted into Bawal tehsil. In 1978 the district comprised 4 tehsils (Mahendragarh, Rewari, Narnaul and Bawal).
Rewari and Bawal tehsils (taken from Mahendragarh district) and Kosli tehsil except 10 villages (taken from Rohtak district) were constituted into a new district of Rewari as on 1st November, 1989. Presently district has 3 sub-divisions (Narnaul,Mahendragarh and Kanina), 5 tehsils (1. Narnaul, 2. Mahendragarh, 3. Nangal Chaudhary, 4. Ateli, 5. Kanina) and 1 sub-tehsil (Satnali)