There isn 't going to be a simple answer to this one!
It will vary from one census to another, for a start.
Then it looks as though Pentre falls into more than one district (using the 1901 census as a starting point).
You might do better to use a resource that allows you to search by address - some subscription websites do, or the 1881 is searchable by address.
HTH
Kind regards, Arranroots
