Monmouthshire on Wikipedia.

Abergavenny.

Bettws Newydd, the church. Generally said to have lost its dedication, some sources suggest it may have been to St. Aeddan. Two interior views - 1, 2, and the font. SO 3622 0588. All © Chris Stafford (2013). Coflein entry. Grade I listed. The cross in the churchyard is also listed, as grade II. © Chris Stafford (2013).
Buckholt, St. John. © Eirian Evans.

Caerwent, St. Stephen and St. Tathan. Interior view. Link. Evangelical Church. All © Gerard Charmley (2010).
Caggle Street, Cwmerra Baptist Chapel. © Janet Gimber (2014).
Caldicot, St. Mary. © Margaret Woodley. Link. Grade I listed. St. Paul (R.C.) on Longcroft Road. © Janet Gimber (2015). Link. Elim Pentecostal Church on Longcroft Road. © Janet Gimber (2015). Methodist Church off Jubilee Way. © Janet Gimber (2015). Link.
Chepstow.
Coed-y-Paen, Christchurch. Another view. Both © Janet Gimber (2016). Link.
Crick, St. Nyveyn's Chapel. On a C11 site, the building is C13, or post-medieval, according to source consulted. It was in agricultural use until the 1980's, when it was converted to residential use. © Janet Gimber (2015). The owner has posted a photo of the interior on flickr, looking towards where the altar would have been. Janet would also like noted her appreciation to the owner for the helpful reception she received on her visit.
Cwmyoy, St. Martin. Much of the church building's history has been a battle between sinking foundations and the ingenuity of masons and architects. Two additional views - 1, 2, and an interior. All © Janet Gimber (2014). Link. Grade I listed.

Dixton, St. Peter. Another view. SO 5197 1357. Both © Janet Gimber (2019). Link. Coflein entry. Grade II* listed.

Forest Coal Pit, Chapel. © Gerard Charmley (2011).

Gilwern, St. Elli. U.R.C. Hope Baptist Chapel (1876). All © Peter Morgan (2011).
Glascoed, Mount Zion Baptist church. Its Coflein entry dates it to 1821. SO 3406 0072. © Janet Gimber (2020).
Govilon, Christ Church. Link. Llanwenarth Baptist Chapel. Janet advises that this is allegedly the oldest Baptist fellowship in Wales, founded 1652, with the first chapel being built on the site in 1695. A plaque records that the present building was renovated in 1870. The village website says that parts of the original building still survive. Another view. SO 2667 1375. All © Janet Gimber (2014).
Grosmont, St. Nicholas. The octagonal tower and spire are unusual. From a postcard in Reg Dosell's Collection. A modern view, © Gerard Charmley (2011).

Henllan, Baptist Chapel. The sign above the door reads "Baptist Chapel Re-built 1805". Interior view. Both © Gerard Charmley (2011).

Llanarth, St. Mary and St. Michael (R.C.), in the grounds of Llanarth Court Hospital. Another view. Both © Janet Gimber (2016). Link.
Llanbadoc, St. Madoc (C). Another view. Alfred Russel Wallace, the naturalist, was baptised here. Both © Chris Stafford (2013). Link. Grade II* listed.
Llandegveth, the former St. David (CiW), now a private residence. St. Tegfedd (CiW), founded in the 7th century. Interior view. All © Gerard Charmley (2010). Link.
Llandogo, St. Oudoceus. Interior view. © Gerard Charmley (2011). Another view, © Peter Morgan (2012). Link. The former Hephzibah Chapel (1882). © Gerard Charmley (2011).
Llanfihangel-near-Rogiet, St. Michael and All Angels, now in the care of the Friends of Friendless Churches. Interior view, the font (claimed by some to be one of the earliest and largest in the county), and the preaching cross in the churchyard. All © Janet Gimber (2015). Link. Grade II* listed.
Llanfihangel Tor-y-Mynydd, St. Michael. SO 4642 0183. © John Gimber (2017). Link1, which has interior photos. Link2.
Llanfrechfa, All Saints. © Janet Gimber. Link.
Llangybi, St. Cybi. ST 3741 9669. © Janet Gimber (2016). Link. Grade II* listed.
Llanover, Hanover Chapel (U.R.C.), originally built as a Welsh language chapel by Lady Llanover. © Gerard Charmley (2010). The former Welsh Presbyterian Church, now a day retreat centre. © Gerard Charmley (2011).
Llanthony, the Priory. SO 2887 2788. From an old postcard in Steve Bulman's Collection. Three modern views - 1, 2, 3, all © Gerard Charmley (2010). Four more views - 1, 2, 3, 4, all © Christopher Skottowe (1964). Link. Grade I listed. St. David. Another view, and an interior view. SO 2884 2782. All © Gerard Charmley (2010). Link1. Link2. Grade I listed.
Llantilio Crossenny, St. Teilo. Interior view (note the doorway in the wall, former access to a gallery, and better seen here), and a superb carved stone slab, set into the floor, all © Janet Gimber (2014). Link. Grade I listed.
Llanvetherine, the former Ebenezer Primitive Methodist Chapel (1842 - date-stone - though not, I suspect, original), now a private residence. © Janet Gimber (2014).

Magor, St. Mary the Virgin (the parish church). Ebenezer Baptist Church. What was a possible former chapel, now a wool shop, has been identified as a former Temperance Hall by Janet Gimber. All © Gerard Charmley. The former Methodist Chapel on Main Road, now in residential use. Another view. Both © Janet Gimber (2015).
Mathern, St. Tewdric. © Margaret Woodley. The sun-dial - most unusual! © Janet Gimber (2014). Grade I listed.
Monmouth.
Mounton, St. Adoenus. Another view, and a window. All © Janet Gimber (2015). Link.

Pandy, Zoar Baptist Chapel. Steps lead down to the river for baptisms. The derelict Hope Calvinistic Methodist Church (1855). Interior view, and the pulpit. All © Gerard Charmley (2010).
Pen y Cae-Mawr, a ruinous General Baptist Chapel stands a few kilometres away at ST 425 972. Old maps show it as Pen Y Well Chapel. Long derelict, Neil advises that since he took these photos, the tombs in the graveyard have been re-located to a field a little distance away. Apparently there were plans to consolidate and rebuild into a private residence, but after initial works, further efforts stopped. The chapel itself must be quite old as gravestones dated back to the 18th century have been re-located, and a yew tree which stood in the churchyard has been destroyed. Three additional views - 1, 2, 3 and an old monument. All © Neil Floyd.
Penhow, St. John the Baptist. © Janet Gimber (2015). Another view, © Carole Sage (1992). Link. Baptist Chapel, originally Penhow Mission Hall (1909), as the date-stone explains. Both © Janet Gimber (2015).
Penterry, St. Mary. Medieval, with a Victorian restoration, there has been a church here since at least 955 A.D. The altar. Without electricity, illumination is provided by oil lamps. All © John Gimber (2017). Link.
Portskewett, St. Mary. The churchyard has a preaching cross. A blocked doorway in the tower is supposed to be Saxon in date. Two interior views - 1, 2. All © Janet Gimber (2015). Link. Grade I listed.
Pwllmeyric, the former Methodist Chapel on Chapel Lane, now residential. Another view. Both © Janet Gimber (2015).

Raglan.
Rogiet, St. Mary. Link. Grade II* listed. Methodist Church on Ifton Road. Link. Both © Janet Gimber (2015).

St. Arvans, St. Arvan. Another view. Both © Janet Gimber (2014). Link. Grade II listed. The former Independent Chapel (1849), now in residential use. © Janet Gimber (2015).
Skenfrith, St. Bridget. Interior view. Both © Gerard Charmley (2011). Link.
Sudbrook, the scant remains of Holy Trinity, a victim of coastal erosion. ST 5065 8732. All © Janet Gimber (2018). Coflein entry.

Tintern.

Undy, St. Mary the Virgin. © Margaret Woodley. Link.
Usk, St. Mary. SO 3789 0081. From an old postcard in Steve Bulman's Collection. A modern view, © Chris Kippin. In the churchyard is the grave of St. David Lewis (Wikipedia entry). Another view. Both © Janet Gimber (2023). Link. Coflein. Grade I listed. For related listed features, see here. Immediately south of the church stand some remains of Usk Priory. Another view. SO 3791 0078. Both © Janet Gimber (2023). Link. The former U.R.C. (1862) on Castle Parade and Twyn Square was previously Congregational, and before that Independent, and is now in use as an art gallery. Another view. Howard Richter has discovered that the date of closure was before 1982, but has been unable to find a definitive date. SO 3776 0097. Both © Martin Richter (2012). The Baptist Church on Old Market Street, which is dated 1842. © Janet Gimber (2023). Link. Coflein. Grade II listed. The former Methodist Chapel on Maryport Street was built as Wesleyan in 1817, and has been converted into flats. SO 3773 0067. © Janet Gimber (2023). Coflein. St. David Lewis and Francis Xavier (R.C) on Porthycarne Street. Its Wikipedia entry dates it to 1847. Another view. Both © Janet Gimber (2023). Link. Coflein. Grade II listed. A 25" O.S. map of 1901 labels an area north of the right angle change of direction of Four Ash Street as Blackfriars. Unfortunately, neither it, or any other available maps show exactly where the Blackfriars monastic house was located. Genuki, quoting from a directory of 1868, says "There were other monastic houses in the town connected with the Black Friars and the Grey Friars; of the former some traces remain, and of the latter an old Norman gateway and part of a chapel.". Perhaps there was evidence for the council to name a road Blackfriars as having stood on, or close to the monastic site, or perhaps it's just in commemoration of it, hence this photo, © Janet Gimber (2023). Blackfriars Road is centred on SO 3797 0099, but the approximate centre of the area indicated as Blackfriars on the map is SO 3797 0094.