Prince Bocskai had his Hajdús settled, 12/12/1605

The Donation Document, written at Korpona
It was the day when Prince Bocskai István of Transylvania elevated 9,254 Hajdús from the peasantry and gave them collective nobility which was quite similar to the collective rights of the Hungarian Székely border guards of Transylvania.
After the 15-Year-War, the Hajdú-question had to be settled because these fearsome soldiers were causing as many troubles as the foreign mercenaries when they had no money.
It was the interest of the Transylvanian prince to make the Hajdú people admit that they needed peace, too. Also, he needed an always ready and reliable army that was located outside of Transylvania. The Hajdú soldiers could be used effectively either against the Germans or the inner enemy of the prince.
But he had to have them settled, first.

Bocskai allocated his own lands for this purpose in Kálló, Nánás, Dorog, Hadháza, Varjas, Vámospércs, Simán, and in Vid.
Here you can read about one of these settlements, Kálló: 
The collective nobility was a special privilege and the Hajdús could enjoy the rights of the noblemen only as a community. 
On top of that, it was restricted to their appointed area. Yet, they didn’t have to pay taxes and had the right to form a local authority and appoint their judges. They were also free to own their lands. In exchange for these, they had to follow the prince to war.
 
The Donation Document described the coat of arms of the Hajdú people:


More Hajdú soldiers were settled during 1606, it was the time when the towns of Kölesér, Szalonta, and Szoboszló were born. You can read about Szoboszló here: 

https://www.hungarianottomanwars.com/kingdom-of-hungary/hajduszoboszlo/

There were 300 Hajdós settled in Kölesér and in Szalonta while 700  mounted Hajdú soldiers were settled in Kereki and Szoboszló.
Like Prince Bocskai István, the princes of Transylvania also had Hajdú soldiers settled. (Prince Rákóczi Zsigmond and Prince Báthory Gábor)
 Sadly, the Hajdús lost their privileges in the 16th century, except for the six large Hajdú towns. These towns had even the right to send their delegates to the Diet of the Kingdom of Hungary in the 18th century.
There was a reform in 1880 when the frames of Hajdú County took shape, now it is called Hajdú-Bihar County in Hungary. 

(Source: Szibler Gábor)