Xanthoria parietina, a conspicuous orange foliose lichen, has been doubtfully recorded as part of the Ontario lichen flora because the previous documented reports were very old (1868 and 1917) and it had never been reported since. Here, we document a number of new sightings, all in southern Ontario. A previous report of this lichen from “Longulac” that was interpreted as Long Lake in Frontenac County is corrected to Longlac in the Thunder Bay District, and the specimen proved to be Xanthomendoza hasseana. A search for the lichen around Belleville, one of the original localities, proved fruitless. It is still not clear whether the new sightings of Xanthoria parietina represent a reintroduction of this coastal species to the inland sites, or whether the lichen has persisted in southern Ontario for almost 140 years, but was never reported. Substrate enrichment (eutrophication due to agricultural activity) in the region is one explanation for the spread of the lichen in southern Ontario.