Hello Haydon

The only John Williams I found in Gwnnws area on 1841 is this:
Blaencwm
John Williams age 75 Male Servant, but not born in County
HO107 Piece 1374 Book 1 ED 6 Folio 17 Page 1
Although the age could be a fit for your John (because ages rounded down up to 5 years in 1841), it is such a common name that is is unlikely. John would have been about 80 years old and Ann in her late 70s so they are likely to have died before 1841.
Kind Regards
Morgan