The region, originally populated by Baltic Old Prussians who were Christianised, became a favoured location for immigration by (later mainly Protestant) Germans (see Ostsiedlung), as well as Poles and Lithuanians along the border regions.
Daerah Prusia yang dulunya ditinggali oleh orang Baltik Prusia Lama yang di-Kristenkan, menjadi lokasi favorit bagi para imigran Orang Jerman (Ostsiedlung,nantinya kebanyakan pemeluk Protestan), juga Orang Polandia dan Orang Lithuania di daerah perbatasan.