Cors Fochno (Welsh pronunciation: [kɔrs ˈvɔχnɔ]) is a raised peat bog near the village of Borth, in the county of Ceredigion, Wales. Lying on the south side of the Dyfi estuary, it forms a component part of the Dyfi National Nature Reserve. It was designated a UNESCO biosphere reserve in 1976, and is the only such reserve in Wales. A boardwalk leading from the northern edge of the bog skirts the edges of the bog and surrounding woodland.

A significant portion of the 264 hectares (652 acres) former peatland complex was taken for agriculture; the surviving core area supports the largest expanse of primary near-natural raised bog in an estuarine context within the United Kingdom.

• Bogs. Marshes. Water fringed vegetation. Fens (85%)
• Heath. Scrub. Maquis and garrigue. (9%)
• Humid grassland. Mesophile grassland (5%)
• Improved grassland (1%)

Part of the Dyfi National Nature Reserve, Cors Fochno contains several varieties of peat moss and carnivorous plant.

Otters, red kites, common buzzards, peregrines and, in the winter,hen harriers can be found here together with a number of Welsh Mountain Ponies, and adder, badger, blackcap, Dartford warbler, fallow deer, nightingale, nightjar, willow warbler, and woodcock. The site holds a population of rosy marsh moth, a very rare species in the UK. The site holds significant populations of Eriophorum angustifolium, the common cottongrass, as well as Round-leaved sundew, all visible from the boardwalk which skirts the northern edge of the bog. In 2019, an extremely rare species of orchid for Great Britain, the Irish Lady's-tresses, was found on the bog. The population has persisted into 2024

• Borth, Borth bog, and the Borth railway station form the backdrop to the main storyline in Season 1, Episode 4 ("The Girl in the Water") of Y Gwyll (Hinterland in English), transmitted on S4C in 2013 and BBC1 Wales in January 2014.
• Cors Fochno, and Borth and its surroundings also form the backdrop to the young adult classic novel and Newbery Honor Book winner, A String in the Harp, 1976, by Nancy Bond.

• www.geograph.co.uk : photos of Cors Fochno and surrounding area
• Cors Fochno Dig: bbc.co.uk/wales
• Joint Nature Conservation Committee