A strong patriotic imperative fuelled Iolo's antiquarian work, but he is also remembered for the overt regionalism of his writings, especially those on bardism. As a young man, he described Glamorgan as the garden of Wales; in his eyes its landscape was more beautiful and its people more sophisticated than those of any other county in Wales. One of his most common sayings was 'Mwynder Morganwg' (the gentleness of Glamorgan). This idealized and Romantic vision of Glamorgan was one of the most prominent themes of his early poetry: 'Y Bardd yn Dychwelyd i Forgannwg wedi bod Flynyddau lawer yn Lloegr'.
However, the tenor of his regionalism changed, and in middle age he expressed it by denigrating north Wales in general, and Gwynedd in particular. This opposition to the north formed an aggressive counterpoint to the merry Glamorgan of Iolo's youthful imagination. (See, for example, his comments on the primacy of south Wales and his sarcasm for Lewis Morris's work.)
An underlying rivalry between north and south Wales has always existed in Wales, but Iolo's hatred of north Wales was a defensive response to the prejudice which he encountered among northerners in the London-Welsh societies. His bitterness towards north Wales deepened when his friendship with Owen Jones (Owain Myfyr) and William Owen Pughe finally dissolved.
As a result, he created a regional hierarchy in his bardic vision: bardism elevated 'civilized' south Wales above 'barbarous' north Wales. It elevated 'civilized' Glamorgan above 'barbarous' Gwynedd. Indeed, Glamorgan was the geographical centre of bardism, and the people and places of the county enjoyed a privileged position within his bardic vision: not only did they inspire Iolo's romantic and druidic fantasies, but they too were transformed by his fertile imagination.