Tregeiriog (a Welsh name translating roughly as "settlement [on the] River Ceiriog") is a village in Wrexham County Borough, Wales.

Richard Jones Berwyn (1838–1917), one of the founders of the Welsh settlement in Patagonia, was a native of the village.

[1] The village of Tregeiriog and the surrounding area were transferred to the parish of Llanarmon Dyffryn Ceiriog in the late 1980s.

Tregeiriog was also in the corresponding civil parish of Llangadwaladr; subsequent to the 1972 Local Government Act it was placed in the community of Ceiriog Ucha.

The cartographer Samuel Lewis, in his 1849 edition of A Topographical Dictionary of Wales, recorded that "the inhabitants have a tradition, that there were formerly a church and a considerable town at Tregeiriog; and in ploughing the land, quantities of large paving stones have been thrown up at different times, which seemed to have been placed in regular order: the name of a farm, Pen-yr-hôwl, the "head of the street," is also adduced in corroboration".