Sonbhadra or Sonebhadra is the 2nd largest district of Uttar Pradesh, India. The district has an area of 6788 km² and a population of 1,862,559 (2011 census), with a population density of 270 persons per km². It lies in the extreme southeast of the state, and is bounded by Mirzapur District to the northwest, Chandoli District to the north, Kaimur and Rohtas districts of Bihar state to the northeast, Garhwa district of Jharkhand state to the east, Koriya and Surguja districts of Chhattisgarh state to the south, and Singrauli district of Madhya Pradesh state to the west. The district headquarters is in the town of Robertsganj. It is the only district in India which borders four states namely Madhya Pradesh, Chhattisgarh, Jharkhand, and Bihar.