It possibly came from vihor, the Serbian and Ukrainian word for "whirlwind" (вихор), or Slavic biela hora, meaning "white mountain".

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.

[citation needed] In 1938, King Carol II promulgated a new Constitution, and subsequently he had the administrative division of the Romanian territory changed.

[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.

[citation needed] Bihor is one of the wealthiest counties in Romania, with a GDP per capita well above the national average.

According to the 1930 census data, the county population was 510,318, ethnically divided among Romanians (61.6%), Hungarians (30.0%), Jews (4.3%), Czechs and Slovaks (2.2%), as well as other minorities.

[10] The county's urban population consisted of 102,277 inhabitants, 54.8% Hungarians, 26.4% Romanians, 15.4% Jews, 1% Germans, as well as other minorities.