Mahendergarh district was formed in 1948 by grouping different tracts of erstwhile princely states; Narnaul and Mahendergarh tehsils from Patiala State, Dadri (Charkhi Dadri) from Jind State and a part of Bawal nizamat from Nabha State. The headquarters of the district are at Narnaul.

Location: The district lies between north latitude 27 0 47 to 28 0 26 and east longitude 75 0 56' to 76 0 51'. It is bounded on the north by Bhiwani and Rohtak districts, on the east by Rewari district and Alwar district of Rajasthan , on the south by Alwar, Jaipur and Sikar districts of Rajasthan, and on the west by Sikar and Jhunjhunu districts of Rajasthan. It has 2 tehsils of Narnaul and MahenderGarh.

Origin of the name of the district: The Mahendergarh town was previously known as Kanaud which took its name from the Kanaudia group of Brahmans. It was founded by Malik Mahdud Khan, a servant of Babur. There is a fort at Mahendergarh which was built by Maratha Ruler, Tantia Tope during the 17th century. This fort was named as Mahendergarh in 1861 by Narinder Singh, the ruler of the erstwhile princely state of Patiala, in honor of his son, Mohinder Singh and consequently the town came to be known as Mahendergarh. The name of Narnaul Nizamat was changed to "Mohindergarh Nizamat".