Slavic paganism
The term "Ruthenia" can refer to Kievan Rus', Novogrodian Rus', or Volynians and other Ruthenian, east Slavic countries and tribes. Paganism survived among the Eastern Slavs the longest time without being baptized. The baptism of Kievan Rus', toke from the hand of the Byzantines, didn't end Paganism in this country, although it caused paganism to become less popular, and a many people didn't admit to practicing Slavic beliefs. Vladimir the Great started the mass baptism of people in Dnieper, which didn't end paganism among people. The family of Vladimir was officially baptized, but still practiced paganism for  a long time. There still existed Ruthenian tribes that were pagan, for example Volynians or White Croats. The last pagans survived maybe even to XIII century.