So far it’s almost perfectly 50/50 yes/no, with every district voting No at a 60% majority except the capital region, which receives two administrative districts due to its (relatively) enormous population. Reykjavik votes 55% in favor and thus outweighs the rest of the country combined.
If the referendum passes, Iceland must first devise the EU agreement, then pass it in parliament as a constitutional amendment. Then, following a general election, the new parliament must pass the agreement again for it to become law.
Ah yes, the last country to join the EU, not long before the bloc’s inevitable collapse. I know this because I read it in a future history book.