It was developed in the 19th century from the (now extinct) Llanllwni, the Shropshire, Welsh Mountain, and Clun Forest breeds.

The Llanwenog's native locale is the Teifi Valley, in western Wales, but it has since spread into other areas.

The wool is of high quality with a Bradford count of 56/58 and a staple length of 7.5 cm (3 in).

[3] The number of purebred Llanwenogs has been decreasing over the last few years and there were estimated to be fewer than three thousand registered breeding ewes in 2015.

[3] The breed appears regularly at agricultural shows in Wales and England.