"Islantilainen" means one's nationality. "I am from Iceland" you can say a few different ways:
- Tulen Islannista. = lit. "I come from Iceland."
- Olen kotoisin Islannista. = "I hail from Iceland."
The latter English one I've never heard before and I'm not sure if it can be used about countries. The Finnish word is hard to explain, it contains two words: 'olla' + 'koti' = 'to be' and 'home', and it basically means that "one's home place is (somewhere)", but I can't do better translation than that, it's just one of these Finnish words and sayings that don't really translate into English. But that is still the most common way of saying where you're from in Finnish :)