Rajko Preradović's ancestors first settled in an area around Grubišno Polje, some 30 kilometers south-east of Bjelovar in Habsburg Military Frontier. Son of Grenz infantry officer Stepan Depreradović, Rajko followed his family's military tradition and joined the Military Frontier as a young man. His family was given Habsburg nobility in the seventeenth century for their military service to the crown and began using the Nobiliary particle. He became a Pomorišje border, lieutenant colonel, before heading one of two convoys of colonists in Imperial Russia in 1752. The other convoy was headed by Jovan Šević.
