Prior to World War I, the territory of the county belonged to Austria-Hungary and was identical with the Csík County of the Kingdom of Hungary. The territory of Ciuc County was transferred to 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.
In 1938, King Carol II promulgated a new Constitution, and subsequently he had the administrative division of the Romanian territory changed. 10 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. Ciuc County became part of Ținutul Mureș.
In 1940, the county was transferred back to Hungary with the rest of Northern Transylvania under the Second Vienna Award. Beginning in 1944, Romanian forces with Soviet assistance recaptured the ceded territory and reintegrated it into Romania, re-establishing the county. Romanian jurisdiction over the county per the Treaty of Trianon was reaffirmed in the Paris Peace Treaties, 1947. The county was disestablished by the communist government of Romania in 1950, and not re-established in 1968 when Romania restored the county administrative system.
In 1930 the urban population of Ciuc County was 15,162, which included 83.8% Hungarians, 8.1% Romanians, and 5.6% Jews by ethnicity. The religious mix of the urban population was 78.9% Roman Catholic, 5.9% Jewish, 4.5% Greek-Catholic, 4.2% Reformed, 4.0% Eastern Orthodox, and 1.2% Armenian Catholic.
