"GROSMONT, a parish in the hundred of Skenfreth, county Monmouth, 9 miles N.E. of Abergavenny, and 10 N.W. of Monmouth. It is, situated in the N.E. part of the county, close upon the borders of Herefordshire, at the foot of Graig Hill. The river Monnow flows through the parish. Grosmont was formerly a market and corporate town, governed by a mayor and other municipal officers; but for many years the market has declined, and the above offices only exist in name. Numerous remains of stone causeways intersect the adjoining meadows, supposed to indicate the site of former streets." [Description(s) from The National Gazetteer of Great Britain and Ireland (1868)
Guide to Monmouth and the various objects of interest in and around it : including brief historical and descriptive notices of Monmouth, Raglan, Whitecastle, Skenfrith, and Grosmont Castles, Tintern Abbey, &c.Monmouth : published by R. Waugh, [18--?] 77p.
Levett, F G. The story of Skenfrith, Grosmont and St. Maughans with excursions to Llangattock-Vibon-Avel and Llanrothal. s.l.] : F.G. Levett, 1984. 250 leaves.
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.
There is no entry in the above for Grosmont parish, whether by omission or otherwise is unknown
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 SO404242 (Lat/Lon: 51.913126, -2.867878), Y Grysmwnt / Grosmont which are provided by: