Over 26,100 records of lichens present in 144 U.S. national park units were assembled from various sources into a database and analyzed. Within these 144 park units 2,435 species and 375 genera are reported, representing 63% and 74% of the North American flora, respectively. The park units are located in 41 states and Washington, D.C. The average number of species in a park is 104, but the median is 60, indicating there are many parks with a small number of species and a few with high numbers. Isle Royale National Park has the most species, 611, and twelve parks have only one species reported. The number of records of lichens present ranged from one for 25 parks, to 1,623 for Isle Royale. Physcia aipolia is the most frequently observed species, being found in 65 parks. One fourth of the park units are classified cultural resource parks, while the remainder are considered natural resource parks. This study was based on 453 sources, including literature citations, park reports and collections in the University of Minnesota Herbarium.