Cluj County (kluʒ) is a county (județ) of Romania, in Transylvania. Its seat is Cluj-Napoca.
In Hungarian it is known as Kolozs megye. Under the Kingdom of Hungary, a county with an identical name (Kolozs County, Comitatul Cluj) existed since the 11th century.
Cluj County lies in the northwestern half of the country, between parallels 47°28' in north and 46°24' in south, meridians 23°39' in west and 24°13' in east, respectively. It covers an area of 6,674 km2 unfolded in the contact zone of three representative natural units: Apuseni Mountains, Someș Plateau and Transylvanian Plain. Cluj County is the 12th largest in the country and occupies 2.8% of Romania's area. It is bordered to the northeast with Maramureș and Bistrița-Năsăud counties, to the east with Mureș County, to the south with Alba County, and to the west with Bihor and Sălaj counties.
The relief is rugged, constituted mostly of hilly units belonging to Someș Plateau and, to a lesser extent, of mountain portions that represent the northeastern part of Apuseni Mountains. Fields are missing on the territory of Cluj County, being replaced, as step of relief, by well-developed terraces and floodplains in the lower sectors of Someșul Mic and Arieș rivers. The hilly area, extended in the central northern and southern part of the county, include several subunits of Someș Plateau (Cluj, Feleacu, Dej hills), among which are individualized numerous depressions (Apahida, Bonțida, Gilău, Dej, Turda, Câmpia Turzii) at the edge of which there are some contact depressions (Huedin and Iara), at the limit of the mountain. The mountain sector, located in southwest, belongs to Apuseni, mountains group of Western Carpathians, represented by sectors of Vlădeasa Massif (peak Vlădeasa – 1,836 m), Gilău Mountains and Muntele Mare, as well as narrow portions of Trascău, Plopiș, Meseș and Bihor mountains. In the eastern part of Cluj County, east of the river alignment Valea Florilor–Maraloiu–Someșul Mic, is located a part of the Hilly Plain of Transylvania, a special unit of relief, with mountainous character, partially overlapped by some gas-condensate domes.