The River Teifi in Wales forms the boundary for most of its length between the counties of Ceredigion and Carmarthenshire, and for the final 3 miles (4.8 km) of its total length of 76 miles (122 km), the boundary between Ceredigion and Pembrokeshire. Its estuary is northwest of Cardigan, known in Welsh as Aberteifi, meaning 'mouth of the Teifi'. Teifi has formerly been anglicised as "Tivy".

Ceredigion ( ), historically Cardiganshire, is a county in the west of Wales. It borders Gwynedd across the Dyfi estuary to the north, Powys to the east, Carmarthenshire and Pembrokeshire to the south, and the Irish Sea to the west. Aberystwyth is the largest settlement and, together with Aberaeron, is an administrative centre of Ceredigion County Council.