The story is actually that of 2 incidents that happened in the village of Possega, either in modern day Croatia or Serbia. I cannot give you an exact location because there no such village listed on the maps yet the closest matches are in above listed countries – in case the name wasn`t changed in the centuries that followed.
The first incident occurred in 1721 when villagers were infected by vampires in the shape of snakes and eventually died a couple of days later being drained of blood.
About 3 weeks after they died, because the disease seemed to be spreading, the elders decided to open the graves of the recently deceased and examine them.
Upon finding a specific family whose members looked undecayed and the bodies were not in the specific position they were buried in, the proceeded to put a stake through the heart of the man [head of the family probably assumed to be the head of the “vampire family”].
Then all the corpses were decapitated and cremated, and their ashes were buried in their graves.
Years passed and everything seemingly returned to normal, however in 1730 we are told that the snake shaped vampires stuck again – this time feeding on a sheep.
A local found the animal on the hills and took it home. There the sheep was slaughtered [presumably this is when they noted the lack of blood in the animal] and the family feed on the meat.
The man, his wife, and two of their children, got sick and died, therefore the elders opened the graved for this family as well. They proceeded to the same ritual and the vampires are never mentioned again.