From the text:
In accordance with this rule it may safely be assumed that the forefathers of Boston had built the first prison-house somewhere in the Vicinity of Cornhill, almost as seasonably as they marked out the first burial-ground, on Isaac Johnson's lot, and round about his grave, which subsequently became the nucleus of all the congregated sepulchres in the old churchyard of King's Chapel.
"... the site on which the venerable structure of King's Chapel has since been built. It had the graveyard, originally Isaac Johnson's home-field, on one side..."