There might have been a chapel of ease in the parish, but just one parish church. My guess is that it was located somewhere in the townland of Haggardstown, and the parish is named after it.
The RC parish covers a number of civil parishes, one of which is Ballybarrack, and this also contains a townland named Ballybarrack... I suspect that B Barrack is an abbreviation of this.
The townland of Ballybarrack is about 8km North West of Blackrock town - see :
Ballybarrack townland (OSI map - check the 6" option for a c1840s map)
Shane