I believe the Austin plant is owned/operated by Flex / Flextronics. Although I see some news blurb that Apple are building a campus out there too, so perhaps that's going to change in the future? As I understand it, it's all contracted out in various places - save Cork as one very odd exception.
For the UK - possibly. The only product I'm aware of, is that they build configure-to-order iMacs. I have no idea how far they distribute from there, but I think it's a safe assumption that they don't maintain this facility just to ship CTO iMacs to Ireland. So I'd consider the UK a safe bet, and most likely most of EMEA. Could they be shipped from China? Most probably - my CTO MBP was. I have no idea what their reasoning is. (Although I'm almost certain it's not all they do in Cork - they have a second campus in the city centre, which wouldn't make sense for manufacturing.)
But for Cork being a foothold into the EU - Cork is their EU headquarters. The company operating there is Apple Distribution International Ltd, not Apple Inc. This is a large factor in how the finances are set up (at least as I understand it) - a mac sold in the UK goes on the books at ADI Ltd, Ireland - not Apple Inc, Cupertino. And this is how "Apple" ends up holding huge amounts of cash outside of the US. Their right hand is an American company, but their left hand is an Irish company. So the US only taxes them on funds held in their right hand.
If you're in Europe, and you have any email receipts from buying things from the mac/ios app stores - scroll to the bottom and check the address. There's a very strong chance it's not Cupertino.
While I'm on a ramble - I also find it curious that Apple don't have a single physical retail presence in Ireland. There's an Apple store in Belfast, but not in Dublin - despite Dublin having 5x the population. I have a strong suspicion this is not a coincidence either.
(I have absolutely no relationship with Apple other than as a customer - this is all just my understanding based on paying attention, and absolutely no inside knowledge. Obviously, else I'd be screwed right about now, eh?)