Hajdú, formerly known as Hajdúság, was an administrative county (comitatus) of the Kingdom of Hungary. The capital of the county was Debrecen. The territory of the county is now part of the Hungarian county Hajdú-Bihar.
The Hajdúság region had a special status in the Kingdom of Hungary, but was turned into the proper county Hajdú in the 19th century. At the 1950 county reform, it was merged with Bihar County (the Hungarian part of pre-Trianon Bihar County) and some smaller parts of the former Szabolcs County to form Hajdú-Bihar County, with its capital at Debrecen.[1]