Hajdu was an administrative county of the Kingdom of Hungary. It had a population of over 13,000 Jews in the early 20th century.
Hungarian antisemitic laws 1938 caused many businesses to close, and in 1939 many Jews were enslaved and sent to Ukraine, where many died in minefields.
The capital of the county was Debrecen. In 1940, the Germans estimated that 12,000 Jews were left in the town. German forces entered the city on 20 March 1944, a ghetto was established by May 1944. The majority of Jews from Debrecen were deported to Theresienstadt ghetto in Czechoslovakia or to Auschwitz-Birkenau concentration and extermination camp in occupied Poland. Some 4,000 Jews from Debrecen survived the war, creating a community of 4,640 in 1946, the largest in the region.