The church of St Faith was originally a separate building from St Paul’s cathedral and was the parish church the stationers who lived in St Pauls churchyard and for the residents of the nearby street of Paternoster Row. The dedication is to St. Faith, the virgin martyr of Aquitaine, who suffered martyrdom in the time of Diocletian. So we can assume there was some French influence at the founding of the church. In 1256 this building was demolished to make way for the eastern expansion of the Cathedral. So the parishioners are given their own space inside the crypt of the cathedral where they could worship instead. So in 1381 it is recorded as “St Faith within the monastery of St Paul’s, London”.
The map below shows the parish of St Faith’s and that of St Gregory by St Paul’s which was on the opposite side of the cathedral (south). In 1644 Hollar produced a print of St Faith in the crypt of old St Paul’s ( see below). However, when St Pauls was destroyed in the Great Fire in 1666 the parish was united with the next door parish of St Augustine Watling Street. St Augustines was destroyed by bombs in the Second World War and now only the tower remains. That parish was combined with St Mary le Bow.
So what can we find today of a church building that was demolished more than 750 years ago? There are still a few remaining physical reminders. First is the pump in St Pauls Courtyard erected by the parishioners of St Faiths which you can still see, although access is difficult because it its behind an iron fence. Second, there are two parish boundary markers – one in New Change and the other in Amen Corner shown below.
The wikipedia page for St Faiths is here