Populate column for list of towns

=IF(ISNA(vlookup(A3,$x$1:$y$100,2,false),"",vlookup(A3,$x$1:$y$100,2,false))

thanks, this works, but do you know how i can use this in multiple rows,
I trie copying and pasting but this completely slows down excel and even freezes as there are over 45,000 records.

Can you suggest a way to make it quicker if at all possible?

Thanks in advance

Can you help?