My reading indicates that in most places pagan beliefs ran right alongside Christian ones, at least as far as common folk were concerned...and this right up to recent times. Good book "The Horse of Pride" written by a Breton gentleman about his boyhood in a small village in Brittany around WWI.

He writes at one point about the people speaking of the "other horned devil" meaning the celtic deity Cernunnos. And about the priests still trying to get the people to stop believing in such things. There is a 50 year period in Brittany (late 1600s/early 1700s IIRC) called The Missions when the Jesuits came in force and took over all the parishes in a full out effort to eradicate such beliefs...didn't work.

A lot of Irish folk would staunchly affirm they are Christian, but believe in leprechauns as well.

Ever spill salt and throw a pinch over your left shoulder?

Then there is all the pagan stuff that Christianity incorporated, from holidays to turning local gods into saints...St. Brigid(sp?) in Ireland is a good example.