Many people have migrated to and from Bagillt over the centuries. In the Dark ages Bagillt was at times in the Saxon Kingdom of Mercia but it is probable that most of the local population would have been Welsh. The biggest changes in population and population movement occurred in the nineteenth century industrial expansion.
With the expansion of coal working (there were 11 known coal pits in Bagillt), there was an increase in workers from other parts of north east Wales and particularly, from Staffordshire, England. During the seventeenth and eighteenth centuries, much emigration from Wales took place, particularly to the colony of Cambria in Western Pennsylvania, in what is now the United States of America. The first notable movements of population from Bagillt took place in the latter half of the nineteenth century. Many left Bagillt to seek their fortune in the Australian goldfields, while the emergence of new nationalist ideals for a free Welsh homeland led to migration to Patagonia, Argentina, where they settled on the edge a lake in the Andes near the town of Trefelin. The town is named Llyn Bagillt, so it is likely that settlers from Bagillt arrived there.