Upvote:1
Dublin Airport FAQ states :
Do I have to go through US Preclearance for a connecting flight?
If you are travelling from Dublin to the US on your connecting flight you can use the US Preclearance facility in Dublin and will not have to go through US customs when you land.
If you fly from Dublin to another airport outside of the US then you will not use US Preclearance.
So yes, you will have to pass through Preclearance