Rosguill (Irish language and official name: Ros Goill) is a peninsula situated in north-north-west County Donegal, Ireland. Lying between the peninsulae of Fanad to the east and Horn Head to the west, Rosguill is a dichotomy of heathland and ocean. With the great Sheephaven Bay with its mellow waters and pure-white strands on the one hand, and the treacherous sand banks of Mulroy Bay on the other. Between, a mixture of bog, hill and pastureland, the ancient walls, remnants of cattle enclosures, and the various evidences of fortification are proof of the area's use since antiquity. The Parish of Rosguill is an alternative name for the Parish of Mevagh, which covers the peninsula and an equally sized hinterland.
There are nearly 800 people living in Rosguill ED and 33% of residents are native Irish speakers.
The area is heavy with legend, the name itself is supposed to have originated, when Fionn mac Cumhaill finally obtained justice by killing Goll mac Morna, the slayer of his father. This act is traditionally said to have taken place at a rock called Carraic Ghoill (English: Carrickguill) lying off the townland of Dumhaigh (English: Dooey). The entire area became known as the "Headland of Goll" or Ros Goill.
Deirdre and Naoise, are thought to have camped on the strand of Trá Mhór (Tramore), when fleeing from Conchobar mac Nessa King of Ulster and his Knights of the Red Branch.
The highest point on the peninsula is Gainne Mhór and its sister peak Gainne Bheag. The name derives from Gráinne, betrothed of Fionn mac Cumhaill and lover of Diarmuid Ua Duibhne. While fleeing Fionn's Fianna warriors en route to Scotland, legend has it that they rested on the hill. Considerable damage to the south western face of Gainne has been the result of unrestrained excavation in recent years. It was also used as a dump for a period. Nach mór a' náire (What a shame).