We report 15 species of Megaloptera from the Interior Highlands of Arkansas, Illinois, Missouri and Oklahoma including 2 genera and 9 species of Sialidae and 4 genera and 6 species of Corydalidae. New state distributional records are reported for Protosialis americana (Rambur) from Illinois, Sialis joppa Ross and S. vagans Ross from Missouri, and Chauliodes pectinicornis (L.) and Nigronia serricornis (Say) from Oklahoma. Distributional and biological data are summarized for each species where available. An illustrated key to the species occurring in the Interior Highlands is included.