Tregarth is a village lying near Thomas Telford's A5 London to Holyhead road between the village of Bethesda and the City of Bangor in Gwynedd, North Wales. The village grew around the local slate industry with many houses being built to house quarry workers and their families. The village is renowned for a street of houses that were built by Lord Penrhyn, proprietor of the Penrhyn Quarry and occupier of Penrhyn Castle to accommodate the workers that refused to strike during the Penrhyn Lockout of 1900-1903. The street, Tanrhiw Road, was known locally as 'Stryd y Gynffon' (Traitor's Row) and was one of the first main settlements in the village based alongside the farmsteads of Ty'n Clawdd, Tanrhiw Isaf and Tahrhiw Uchaf.

Tregarth has a population of some 1000 people of which around 70% would consider Welsh as their first language.

The Village is the birthplace of a number of local luminaries such as the late Sir Ifor Williams, the late Ifor Bowen Griffith, the late T. Gwynn Jones and actor John Ogwen.

Tregarth has its own Primary School, Public House (Pant yr Ardd), Village Shop, Chapel (Shiloh), Church (Santes Fair, St Mary's) and community centre which is the venue for many village activities such as Ysgol Feithrin (nursery school), Youth Club, Clwb yr Henoed (Senior Citizens Club) and Snooker Club.

Owing to Bethesda's industrial heritage, Tregarth has two rail lines running through its centre, one The Bethesda Branch (London and North Western Railway) which was closed in 1963 and the other The Narrow Gauge Penrhyn Quarry Railway Line which was used to transport slate from the Penrhyn Quarries to Port Penrhyn and was closed in 1962. These lines have since been converted to cycle paths as part of Sustrans Lôn Las Cymru cycle route and take the cyclist on a wonderful journey from the beautiful Nant Ffrancon Pass winding through Tregarth down along the River Cegin towards Bangor and the splendour of Port Penrhyn.

The Moelyci Environmental Centre (Canolfan Amgylcheddol Moelyci) can also be found in Tregarth which is a community based centre that specialises in the practice and teaching of environmental matters. The centre runs many open days and activities and welcomes visitors.