Cylch-y-Garn yw cymuned ar Ynys Môn, Cymru, wedi’i lleoli ar arfordir gogledd-orllewin y sir — tua 9 milltir i’r gorllewin o Amlwch, 12.5 milltir i’r gogledd-ddwyrain o Holyhead, a 15 milltir i’r gogledd-orllewin o Langefni. Mae’n cynnwys y pentrefi Llanfair-yng-nghornwy, Llanrhuddlad, a Rhydwyn, ynghyd â Llanrhwydrys, Caerau, a Cemlyn, yn ogystal â phen gogledd-orllewin yr ynys yng Ngharmel Head a’r ynysydd oddi ar y lan, Skerries a West Mouse.

Mae Cyngor Cymuned Cylch y Garn yn cynnwys dau ward: Llanrhuddlad gyda saith cynghorydd cymunedol, a Llanfairynghornwy gyda pedwar. Cynhelir cyfarfodydd ar Ddydd Llun olaf pob mis, o Ionawr tan Orffennaf ac o Fedi tan Dachwedd, ac mae’r cyngor yn gweithredu o dan arweiniad Cyngor Sir Ynys Môn.

Yn ôl cyfrifiad 2001, roedd gan y gymuned boblogaeth o 675, a chynyddu i 758 erbyn cyfrifiad 2011.

Mae Bae Cemlyn, yng nghyffiniau gogledd-ddwyrain y gymuned, yn eiddo i Ymddiriedolaeth Genedlaethol ac yn gartref i warchodfa natur a reolir gan Ymddiriedolaeth Natur Gogledd Cymru. Mae ganddi lagŵn sy’n cael ei wahaniaethu oddi wrth y môr gan arfordir sgleiniog, ac mae’r ynysydd yn cynnig safleoedd nythu i adar fel terns cyffredin, Arctic a Sandwich, gan gynnwys un o’r poblogaethau nythu mwyaf yn y DU o’r olaf.

Mae Eglwys Sant Ffraid yn Llanfair-yng-nghornwy o darddiad canoloesol cynnar, gyda pharcell chancel sy’n dyddio o’r 11eg neu’r 12fed ganrif.

Cylch-y-Garn is a community in Anglesey (Ynys Môn), Wales, located on the north-west coast of the county — about 9 miles west of Amlwch, 12.5 miles north-east of Holyhead, and 15 miles north-west of Llangefni. Wikipedia It includes the villages of Llanfair-yng-Nghornwy, Llanrhyddlad, and Rhydwyn, as well as Llanrhwydrys, Caerau, and Cemlyn, plus the north-west tip of the island at Carmel Head and the offshore islands of the Skerries and West Mouse.

Cylch y Garn Community Council consists of two wards: Llanrhuddlad with seven Community Councillors, and Llanfairynghornwy with four Community Councillors. Meetings are held on the last Monday of the month, from January to July and September to November.It operates under the umbrella of Isle of Anglesey County Council.

At the 2001 census the community had a population of 675, rising to 758 at the 2011 census

Cemlyn Bay, in the north-east of the community, is owned by the National Trust and is home to a nature reserve managed by the North Wales Wildlife Trust. It features a lagoon separated from the sea by a shingle ridge, and its islands provide nesting sites for common, Arctic, and Sandwich terns — including one of the UK’s largest breeding populations of the latter.

St Mary’s Church at Llanfair-yng-Nghornwy is of early medieval origin, with a chancel arch dating from the 11th or 12th century.