Harlech is a seaside resort and community in Gwynedd, North Wales, and formerly in the historic county of Merionethshire. It lies on Tremadog Bay in the Snowdonia National Park. Before 1966, it belonged to the Meirionydd District of the 1974 County of Gwynedd. Its landmark Harlech Castle was begun in 1283 by Edward I of England, captured by Owain Glyndŵr, and in the 1480s, a stronghold of Henry Tudor. Once on a seaside cliff face, it is now half a mile inland. New housing has appeared in the low town and in the high town around the shopping street, church and castle. The two are linked by a steep road called "Twtil". Of its 1,447 inhabitants, 51 per cent habitually speak Welsh. The built-up area with Llanfair had a population of 1,762 in the 2001 census, over half of whom lacked Welsh identity, and the electoral ward which includes Talsarnau 1,997 in the 2011 census. The estimate in 2019 was 1,881. The population of the community, which includes just the village, was 1,263 as of the 2021 census.

Until 1974, Merionethshire or Merioneth was an administrative county in the north-west of Wales, later classed as one of the thirteen historic counties of Wales.