The Credit River Watershed contains a mosaic of habitat types, which support a large number of lichen species; however, no detailed inventories of the lichen diversity in this region exist. We present a checklist of 124 species of lichens and allied fungi discovered in the watershed. We report new collections of Illosporium carneum, Microcalicium ahlneri, and Pseudoschismatomma rufescens, which are provincially rare. In this checklist, twelve species are ranked as S1 (critically imperiled), S2 (imperiled), or S3 (vulnerable) in Ontario by the Natural Heritage Information Centre. Local municipalities and conservation authorities can use these baseline data to help monitor changes in populations and in determining areas of high biodiversity in the watershed.