Part of Salem, Dharmapuri, Krishnagiri and Mysore were together named as Thagadur Nadu in Sangam age. Krishnagiri was once ruled by Adhiyaman and hence also known as Adhiayaman Nadu. Adhiayaman, considered a noble king, offered 'Karunelli' (Goose Berry) to the great Tamil poetess "Avvaiyar", who adorned his court for her long life. This region was ruled by Pallavas, Gangas, Nulambas, Cholas, Hoysalas, Vijaya Nagar Emperors, Bijapur Sultans, Wudayars of Mysore and Nayaks of Madurai. The region of krishnagiri served as gateway of Tamil Nadu and a protective barrier for Southern region defending onslaughts from barriers with motives of imperialism and exploitation. Twelve Forts in this region were popularly known as 'Bara Mahal' Forts. These forts have withstood many attacks by the Mysore and Andhra rulers. Amongst them, Krishnagiri Fort became the first and forth most defensive place. The majestic fort built on the Krishnagiri hill by the Vijayanagar Emperors, stands as testimony even now. Kundani, a place in Krishnagiri District was once the head quarters of the Hoysala King Veera Ramanathan in the 13th Centuty AD. Jagadevarayan, a Hoysala king made 'Jagadevi' (one of the 'Bara Mahal' forts) as his capital.
Till the year 2004 Krishnagiri was a part of the Dharmapuri district. It was then separated from Dharmapuri district and formed as the 30th separate district of Tamil Nadu in 2004.
Krishnagiri district covers an area of 5143 km▓. Krishnagiri district is bound by Vellore and Thiruvannamalai districts to the East, State of Karnataka to the west, State of Andhra Pradesh to the North and Dharmapuri District to the south. This district is elevated from 300m to 1400m above the mean sea level. It is located between 11║ 12'N to 12║ 49'N Latitude, 77║ 27'E to 78║ 38'E Longitude.