Well, Iceland believed in the Norse gods, very pagan, still believe in the elves that live in the rocks. But it seems we have had a weird relationship with Christianity, perhaps of how it was picked up.

I wanted to do a refresh on my knowledge of this, been ages since I learned this in gradeschool, might amuse myself by sharing how Iceland took up Christianity. The event itself is even called Kristnitaka (literally "the taking of Christianity").

The quick story would be that around the year 1000 the king of Norway was pressuring Icelanders to convert, going as far as to denying Icelandic ships access to Norwegian ports and taking several Icelanders hostage (sons of prominent Icelandic chieftains), and the local law speaker made a deal about it, "we shall take Christianity if we can practice our pagan faith in the safety of our homes" essentially, he took a nap under a pelt to think about it, and then declared that this would be our new law about religion. That is how Iceland became publicly Christian but pagan under the hood.

Some like to believe that even local words for things related to Christianity were developed to disrespect the religion, like the word for church is kirkja sounds identical to the word kyrkja (we read i and y the same) which means to strangle someone. Though I don't think it is true, it is just a odd coincidence.

But yeah, Icelanders have always been very casual about the Christian religion because of how it got taken up "You are now Christian, but you can just keep on doing what you were doing before, just not allowed in public".

Though I don't think many actually worship the Norse gods these days, most are essentially atheists or casual Christians. We are usually registered by default as Christians at birth and many don't bother to change that (chosen religion in registry decides where your religious portion of the taxes you pay goes, if I recall correctly).

My older half siblings are very American in their Christianity, maybe because many of them lived over there for some time. Very serious Christians compared to most locals. One of them is even a singer at their church, has published albums with Christian songs, they are pretty good I think.