The Ilocano people of Ilocos Norte in the Philippines have high regard for seaweed use. The traditional seaweed medicines used by them are old and time-tested, albeit little explored. This study examines the selection of seaweeds associated with a defined folk knowledge and their source availability in Ilocos Norte. Thirty-four (34) seaweed species were traditionally perceived as medicinal for eight types of emic indications, almost 80% of which were edible. Three major groups, i.e. rhodophytes (16 spp.), ochrophytes (7 spp.), and chlorophytes (11 spp.), of 12 families and 20 genera constituted the list. Most species were used for digestive, pulmonary, and glandular-related complaints. The Ilocano residing Pagudpud and Burgos were the most familiar in terms of the number of used species. Caulerpa racemosa (ar-arusip) was the most familiar seaweed used as a cough or asthma reliever. Caulerpa racemosa, Hydroclathrus clathratus, and Gracilaria edulis had the highest use value, whereas Codium intricatum, Gelidiella acerosa, and C. racemosa had the highest fidelity level scores. The distribution of taxa in dry and wet seasons markedly varied per site. Gelidiella acerosa was the only species growing on all sites year-round. Correspondence between folk use and phytochemical activity was inferred in nearly all listed species. The information presented here will allow continued validations and tests of folk medicinal seaweeds for new drugs and may bring additional armamentarium to the Philippine pharmacopeia.