I'm glad that was helpful, Justin.
Parents' marriage by banns (not much detail):
<ref>Monmouthshire, Wales, Anglican Baptisms, Marriages and Burials, 1551-1994 [database on-line]. Lehi, UT, USA: Ancestry.com Operations, Inc., 2020. John Williams. Married 18 November 1821 at Chepstow, Monmouthshire, Wales. Residence Place: Chepstow. Spouse: Sarah Mechin. Page number: 57. {{Ancestry Record|62107|603507}}. Retrieved 17 January 2023.</ref>
Ancestry record; sharing link; better image.
That John's christening—his mother's name was Mary:
<ref>"England Births and Christenings, 1538-1975", database, {{FamilySearch Record ark:/61903/1:1:NLJL-DF2}} (19 September 2020), John Williams. Christened 11 November 1798 at St Briavels, Gloucestershire, England. Parents John and Mary Williams. Image not available. Accessed 17 January 2023.</ref>
FamilySearch link (accessible free if you register an account).
There are more sources at this Ancestry tree. Maybe you can access it at your local library.