Hi Margaret
First of all welcome to Rootschat and especially the Sussex Boards - one of the best; and thank you for all those nice compliments.
You just mentioned St John - is that St John Sub Castro or St John the Baptist - both are in Lewes.
I notice that William & Jemima married by license:
Extract from the Sussex Marriage Index:
Archdeaconry of Lewes Marriage Licence, Date: 6 Apr 1815:
Groom: William SIMMONS, bachelor, 20, with consent of father Samuel of the same parish.
Bride: Jemima HARDING, spinster, 18 S.John Sub Castro
Extra Information: SIMMONS Saml. labr All Saints
Marriage
Location: Lewes St. John sub Castro, East Sussex, Date: 6 Apr 1815:
Groom: William SIMMONS, with consent of father Samuel.
Bride: Jemima HARDING, with consent of father John, both of this parish
This seems to indicate it is Sub Castro, but there is a mention of All Saints in Lewes
Chris in 1066