"OLDCASTLE, a parish in the lower division of the hundred of Abergavenny, county Monmouth, 6 miles N.E. of Abergavenny, its post town, and 9 from Crickhowell. The parish, which is of small extent, is situated upon the E. slope of the Black mountains, which skirt the vale of Ewyas near the river Monnow. The village consists of a few farmhouses. The tithes have been commuted for a rent-charge of £48 4s. 6d., and the glebe consists of about 123 acres." [Description(s) from The National Gazetteer of Great Britain and Ireland (1868)
Church and chapel data from The Religious census of 1851 : A Calendar of the returns relating to Wales, Vol 1, South Wales.Ed. by I.G Jones, & D. Williams. UWP, Cardiff, 1976. The names given towards the end of each entry are those of the informants. Check with Gwent RO to see what extant records are held, and possible names of chapels/churches established after 1851.
Oldcastle Parish; Statistics; Area 922 acres; Population 23 males, 24 females, total 47
St James Parish Church Attendance - morning 10, scholars none 1 service in English Theophilus Morgan, Incumbent
Family Search have an interactive map called "England and Wales Jurisdictions 1851" showing parish (and other) boundaries with optional background maps such as Ordnance Survey. There is also a Search facility, do read the guidance notes to get maximum benefit from this useful resource. See here for further background information to assist in the interpretation of this data
Kain, R.J.P., Oliver, R.R., Historic Parishes of England and Wales: an Electronic Map of Boundaries before 1850 with a Gazetteer and Metadata [computer file]. Colchester, Essex: History Data Service, UK Data Archive [distributor], 17 May 2001. SN: 4348. Here is a gazetteer/finding aid plus a set of overview maps to accurately identify the position of parishes within the county.
You can see maps centred on OS grid reference SO324245 (Lat/Lon: 51.914908, -2.984225), Hengastell / Oldcastle which are provided by: