St Cynhaearn, Ynyscynhaearn, is sited in a remote walled churchyard raised above marshland. Designed by John Williams around 1832, it lies slightly east of a previous church known as Ystumllyn chapel. Cruciform in plan, it is rather plain on the outside, but includes an unspoilt interior, with a western gallery, tiered box pews in the north transept, a vestry in the south transept and a shallow sanctuary with pews on each side. There are Ten Commandments and Creed boards above the gilded reredos and the pulpit is three-decked. The plan shows direct access from the vestry, but the executed stair is an elegant curved one from the nave, as is the one to the gallery. The benches and pews have a simple design and the names of the pew-holders are painted on the ends. The organ has a fine early nineteenth century Gothic case, possibly made by Flight & Robson. Originally it was in Tremadog church, but was moved to Ynyscynhaearn in 1854. The stained glass eastern window dates from 1899 and the north transept window to 1906, by Powells. The lychgate has a rough slate roof, rubble walls, and a cast-iron gate. There are eighteenth century slate headstones inside. The churchyard has two mid-nineteenth century railed tombs to members of the Carreg and Pilkington families. A gravestone on the north side of the path is to John Ystumllyn, said to be the first black slave to come to Wales. The pink late-nineteenth century granite tombstones outside the main north door are to John Williams (Ioan Madog) and Ellis Owen, bards. A slate ledger tomb at the western end of the churchyard commemorates David Owen (1709?39), the composer of `Dafydd y Garreg Wen? and an important figure of Welsh harp music.

The church hall dates to 1937 and is by Clough Williams-Ellis. It represents an attempt at a convenient substitute for the old church, built in the vicarage garden. Made from stone, it is rectangular with rounded corners. Sprocketed roofs of small slates ingeniously flow round the corners. The western doorway is in a splayed recess with an oval niche for the bell above, and a square-section Chinoiserie western cupola. The small sanctuary can be shut off by folding doors.

Sources include:
Haslam, Orbach and Voelcker (2009)
The Buildings of Wales: Gwynedd. Pevsner Architectural Guide, page 494.
Richard Suggett, Painted Temples: Wallpaintings and Rood-screens in Welsh Churches, 1200–1800, (RCAHMW 2021)

RCAHMW 2022