Cilymaenllwyd is a community on the extreme northwest of Carmarthenshire in Wales. The community population at the 2011 census was 743. It lies about 25 miles (40 km) west of Carmarthen, 12 miles (19 km) southeast of Fishguard and 19 miles (31 km) northwest of Haverfordwest. The A478 road runs through the community.
Cilymaenllwyd has an area of 2628 hectares and had a population of 725 in 2003. The western edge of the community borders Pembrokeshire. The community is bordered by the communities of Llanboidy and Henllanfallteg in Carmarthenshire; and by: Clynderwen; Mynachlog-ddu; and Crymych, all being in Pembrokeshire. The River Tâf forms the eastern boundary. The area is part of the foothills of the Preseli Mountains rising to an altitude of 248 metres and is dissected by deep valleys of the Tâf and its tributaries.
Historically it was part of Derllys Hundred. In the 20th century the main road through the community, which links Cardigan, Ceredigion in the north to Tenby, Pembrokeshire in the south, was designated the A478.
The principal commerce of the parish is agriculture.
Few maps mark the name Cilymaenllwyd but there are several settlements in the community.
Grid reference SN143266