Bihor County (Romanian pronunciation: [biˈhor] ^ⓘ, Hungarian: Bihar megye) is a county (județ) in western Romania. With a total area of 7,544 km² (2,913 sq mi), Bihor is Romania's 6th largest county geographically and the main county in the historical region of Crișana. Its capital city is Oradea (Nagyvárad).

The origin of the name Bihor is uncertain, except that it likely takes its name from an ancient fortress in the current commune of Biharia. It possibly came from vihor, the Serbian and Ukrainian word for "whirlwind" (вихор), or Slavic biela hora, meaning "white mountain".^{[citation needed]} Another theory is that Biharea is of Daco-Thracian etymology (bi meaning "two" and harati "take" or "lead"), possibly meaning two possessions of land in the Duchy of Menumorut (Ménmarót). Another theory is that the name comes from bour, the Romanian term for aurochs (from the Latin word bubalus). The animal once inhabited the lands of northwestern Romania. Under this controversial theory, the name changed from buar to buhar and to Bihar and Bihor.

The coat of arms of Bihor County was adopted in 1998, and is a quarterly shield featuring a castle (for the Castle of Bihar), five wheat stalks with a ribbon, a grape and a scroll with the text of Deșteaptă-te, române!, covered with a fess featuring three fish. It was subject to redesign in 2013 after it was discovered by a local teacher that the text on the scroll was erroneously written in Greek, rather than Cyrillic (the original alphabet used to write the poem's text) or the Latin alphabet. The county has no significant history with Greece.

This county has a total area of 7,544 km² (2,913 sq mi). In the eastern side of the county there are the Apuseni Mountains, with the highest peak being the Cucurbăta Mare (also known as the Bihor Peak), at 1,849 m (6,066 ft). The heights decrease westwards, passing through the hills an ending in the Romanian Western Plain – the eastern side of the Pannonian plain.

The county is mainly the Criș hydrographic basin with the rivers Crișul Repede (Sebes Körös), Crișul Negru (Fekete Körös), and Barcău the main rivers.

Prior to World War I, the territory of the county belonged to Austria-Hungary and mostly was contained in the Bihar County of the Kingdom of Hungary. After the collapse of Austria-Hungary at the end of the war, and the declaration of the Union of Transylvania with Romania, the Romanian Army took control of the county in April 1919, during the Hungarian–Romanian War. The territory of Bihor County was officially transferred to the Kingdom of Romania from Hungary as successor state to Austria-Hungary in 1920 under the Treaty of Trianon. After the administrative unification law in 1925, the name of the county remained as it was, but the territory was reorganized.^{[citation needed]}

In 1938, King Carol II promulgated a new Constitution, and subsequently he had the administrative division of the Romanian territory changed. Ten ținuturi (approximate translation: "lands") were created (by merging the counties) to be ruled by rezidenți regali (approximate translation: "Royal Residents") – appointed directly by the king – instead of the prefects. Bihor County became part of Ținutul Crișuri.^{[citation needed]}

In August 1940, under the auspices of Nazi Germany, which imposed the Second Vienna Award, Hungary retook the territory of Northern Transylvania (which included part of the county) from Romania. In October 1944, Romanian forces with Soviet assistance recaptured the ceded territory and reintegrated it into Romania. Romanian jurisdiction over the entire county per the Treaty of Trianon was reaffirmed in the Paris Peace Treaties, 1947. In September 1950, the county was disestablished by the communist government of Romania and was replaced by the Bihor Region, whose territory comprised an area similar to the old county. Bihor County was re-established in February 1968, when Romania restored the county administrative system.^{[citation needed]}