A vascular plant survey of Ledges State Park (Boone County, Iowa; 482 ha) was conducted from 2005 to 2008 during which 697 taxa were encountered. A search of the literature and the holdings of Iowa State University's Ada Hayden Herbarium (ISC) revealed 79 additional taxa found in the Park. This total of 776 taxa adds 306 to the floras published in two previous floristic studies of the Park. An annotated checklist was prepared that includes the origin, habitat preferences, and collection history for each taxon. This study reports 31 taxa not included in Eilers and Roosa's 1994 checklist of Iowa's vascular flora, including a population of Oenanthe that may represent a new species. Thirteen taxa documented from the Park are listed as endangered, threatened, or special concern by the Iowa Department of Natural Resources. The results of this survey provide knowledge of the extent of invasive species in the Park and facilitate analysis of floristic change. Survey results also provide a more thorough understanding of Iowa's flora, including updated species' distributions and the status of rare plants. The study reveals the need for a computer database of specimens in Iowa's herbaria and an online, regularly updated checklist of Iowa vascular plants. Like Ledges, many parks fulfill important conservation roles in providing a haven for sensitive species and uncommon plant communities. To ensure the future integrity of all of Iowa's state parks, we recommend increased support for scientific research and conservation.