Anglesey on Wikipedia.

A good churches website for Anglesey.

Aberffraw, St. Beuno (CiW). Largely a Victorian re-build, it still retains some features from the 12th, 14th, and 16th centuries. Another view. SH 353 688. Link1. Link2. Link3. Link4. Seion Methodist Church (1887). SH 354 690. All © Dave Westrap.
Amlwch, dedicated to St. Eleth. The Catholic church Our Lady of the Sea. Both © Bill McKenzie. Methodist Church on Wesley Street, dating from 1832. It was built to serve English miners and their families, who had come to Amlwch to work in the massive copper mine on Parys Mountain. © Keith Alexander.

Beaumaris, St. Mary & St. Nicholas. From an old postcard in Steve Bulman's Collection. A modern view, and an interior view, both © Stuart Mackrell. Link. Our Lady Queen of Martyrs (R.C.). © Tony Preston.
Bryn Du, the former Calvinistic Methodist Chapel, as seen by Streetview in 2021. It's dated 1901, and Coflein says there were predecessors of 1795 (demolished 1859), 1814 and 1859, on this site and another "just 20 feet away". It had closed no later than 2020, when it was being offered for sale (there are interior photos). The other site is shown on a map of 1888 (although it's more than 20 feet away"), across the road and a little further S.E. at SH 3447 7274. Its site was seen by Streetview in 2021. The 1901 building is grade II listed.
Brynsiencyn, Horeb Presbyterian Church. SH 481 671. © Dave Westrap.

Holyhead.

Llanallgo, Paradws Llanallgo (Presbyterian). SH 504 853. © Dave Westrap. Link.
Llanbeulan, St. Peulan, stands alone surrounded by fields, and has been in the care of the Friends of Friendless Churches since 2004. Interior view. The unusual font is possibly pre-Norman. SH 373 754. All © Tim Hollinghurst. Another view, three additional interiors - 1, 2, 3, and the font, all © Iain Taylor. Link.
Llanddwyn Island, the ruins of St. Dwynwen. Its Coflein entry dates it to the 16th century. The Wikipedia entry for the island says that the remains of earlier buildings have been found in archaeological investigations. SH 3869 6276. © Janet Gimber (2023). A map of 1901 shows, a short way south of the church, Llanddwyn Abbey (Benedictine) (Remains of), at SH 3865 6271. It's mentioned here, where there is a Lidar scan showing the monastic earthworks, but it seems to have escaped more general notice.
Llanedwen, St. Edwen (CiW). SH 517 682. © Dave Westrap. Link.
Llaneilian, St. Eilian (CiW). Another view, and two interior views - 1, 2, all © Dave Westrap (2010). SH 469 929. Links (a selection - there are many more. Link1. Link2. Link3. Link4.
Llanfaelog, St. Maelog. Interior view. SH 3369 7299. Both © Tim Hollinghurst. Link. Coflein says that the 12th century font is from St. Mary, Talyllyn. Grade II listed - dates it to 1848, replacing an earlier church on a different site within the churchyard - I haven't found any source which says exactly where the old church stood. About ¼ of a mile N.W. of the church is Rehoboth Independent/Congregational Chapel (2009 Streetview). It's dated 1827. Its Coflein entry (which includes photos) says it was still in active use in 1999, but in 2024 it doesn't seem to have a web presence so may have closed. SH 3345 7327.
Llanfairynghornwy, St. Mary. SH 326 908. © Rick Williams.
Llanfihangel Ysceifiog, the ruins of St. Michael. Another view, and two "interiors" - 1, 2. All © Iain Taylor. Link.
Llangadwaladr, St. Cadwaladr. Interior view. SH 3837 6927. Both © Tim Hollinghurst. Two additional views - 1, 2, the churchyard gate, chancel window, and the altar, all © Martin Richter (2011). Link1. Link2. Link3. Link4. Grade I listed.
Llangeinwen, St. Ceinwen. © Bill McKenzie.
Llangoed, St. Cawrdaf. SH 612 806. Ty Rhys Calvinistic Methodist Chapel. The inscription has dates 1794, 1822, 1878 and 1908. SH 613 806. My thanks to Janet Gimber for the identification. Both © Tony Preston (2009).
Llangwyfan, St. Cwyfan (CiW) is set on the tiny island of Cribinau just off the shore. Also known as "The Church in the Sea". Another view, and another. Services are held only a few times a year. SH 335 682. All © Dave Westrap. Link1. Link2. Link3. Link4.
Llanidan, St. Idan (CiW). SH 489 674. © Dave Westrap. Link.
Llantrisant, St. Afran, St. Ieuan and St. Sannan. Further views show a doorway, the interior, the font, and the box pews. SH 3495 8406. All © Iain Taylor. Link. Grade II* listed.
Lligwy, the ruins of a church (no dedication), also known as Hen Capel (or Gapel) Lligwy. Another view, two "interiors" - 1, 2, and the crypt. SH 4991 8632. All © Iain Taylor. Link. Coflein has many photos, and says it was a chapel of ease to St. Michael at Penrhos-Lligwy (for which, see below). Grade II listed.

Newborough, St. Peter (Church in Wales). SH 419 654. © Dave Westrap. Link.

Penmon, the Priory. From an old illustration (1930's) in Colin Waters' Collection. A modern view, © Penny Salisbury. This old postcard (from Steve Bulman's Collection) shows an ancient cross. Previously in the Unknown section, it was identified by Janet Gimber. SH 6302 8073. Link.
Penrhos-Lligwy, St. Michael, as seen (distantly) by Streetview in 2021. SH 4805 8592. Link. Coflein has several photos. Grade II* listed.
Pentraeth, St. Mary. SH 5237 7844. © Bill McKenzie. Link. Coflein. Grade II listed. For related listed features, see here. A large scale map of 1919 shows two chapels. Capel Ebenezer Independent Chapel (2021 Streetview) at SH 5230 7840. Coflein. dates it to 1903, with three predecessors. The Calvinistic Methodist Capel Nazareth on Chapel Street at SH 5222 7873. Coflein dates it to a re-build in 1860 of a chapel of 1829, closing in 1998, whereafter it "fell into disuse". I think it's this building seen in a Streetview from 2021. Coflein also has an entry for an earlier predecessor on a different site, at SH 5216 7841, dating it to 1855, again with predecessors, and it says it was converted to residential use in 1998. It was seen by Streetview in 2021. Another chapel a little way north of Nazareth appears on a map of 1919, which was revised no later than 1915. Labelled as Capel Moriah (Baptist), its brief Coflein entry dates it to 1902. 2024 Streetview. SH 5222 7898.

Tal-y-Llyn, St. Mary. SH 3666 7287. © Tim Hollinghurst. Two additional views - 1, 2, the interior, and the font, all © Iain Taylor. In the care of the Friends of Friendless Churches since 1999 - link. Grade I listed, says it was made redundant in 1992.
Trefdraeth, St. Beuno. Interior view. SH 4085 7039. Both © Tim Hollinghurst. Link1. Link2. Coflein. Grade II* listed. There are three chapels or chapel sites nearby - Capel Mawr (Independent) at Capel-mawr (SH 4154 7173) - demolished, site on Streetview in 2024, Capel Bethel (Calvinistic Methodist) at Bethel (SH 3969 7035) - 2024 Streetview, and Capel Elim (Wesleyan Methodist) to the south of the village (SH 3983 6947) - 2024 Streetview. The various Coflein entries are as follows - Bethel (re-built 1905 on the site of predecessors of 1866 and 1805). Elim (re-built 1890, originally of 1835, closed 1985 and subsequently converted). Mawr (1773, re-built 1834 and 1871, demolished  "by 1999").