None. Due to the nature of freedom of choice, there is no entirely christian labelled country.
Many countries have adopted their laws and parliament based primarily on Christian principles...
Those countries which have some form of Christianity as their official religion are listed below: Argentina Armenia Costa Rica Cyprus Denmark England Greece Iceland Liechtenstein Malta Monaco Norway...
As far as I know there are 2.1 billion Christians in the world roughly however not counting Catholics there are probably(estimation I made with no information at all) just less than 1 billion...