Island location where herd’s heard? (5)
I believe the answer is:
cowes
'island location' is the definition.
(town on the Isle of Wight)
'herd's heard?' is the wordplay.
'herd' becomes 'cows'.
'heard?' indicates a 'sounds like' (homophone) clue.
'cows' is a homophone of 'COWES'.
'where' is the link.
(Other definitions for cowes that I've seen before include "IOW regatta town" , "English town?" , "where regatta happens" , "Isle of Wight yachting centre" , "Venue for Isle of Wight regatta" .)