Suzanne - The record I find regarding this child seems to indicate that he was buried in 1600, not born.Am I misreading something?
Matthias Cenion a bastard the s. of Willm and Elizabeth Horrocks intra ecclesiam 30 Dec 1600
Lancashire: Bolton - Parish Register, 1587-1660
Also the William St. John you postulate as this William Cenion was born in Wiltshire and died in Hampshire...both quite a long distance from Lancashire where the bastardy took place, esp for the 1600s.
I was very hopeful when I first read your post as I have a feeling that there was some kind of connection between "our" Matthias and Nicholas of Windsor, CT.