Ichthyornis was named by Marsh (1872) [Sepkoski's age data: K Turo K Camp Sepkoski's reference number: 1066]. Its type is Ichthyornis dispar. It is the type genus of Ichthyornithidae, Ichthyornidae.

It was assigned to Aves by Marsh (1872); to Ichthyornidae by Marsh (1873), Marsh (1873) and Marsh (1873); to Odontotormae by Marsh (1880); to Odontotormae by Zittel (1890); to Aves by Bakker (1986); to Ichthyornithidae by Hay (1902), Lambrecht (1933), Wetmore (1960), Carroll (1988), Parris and Echols (1992) and Tokaryk et al. (1997); to Carinatae by Chiappe (2002); to Ichthyornithiformes by Chatterjee (1991), Sepkoski (2002) and Padian (2004); to Ichthyornithes by Marsh (1875) and Clarke (2004); to Euornithes by Cau and Arduini (2008); to Ornithuromorpha by Naish et al. (2012), O'Connor and Zelenkov (2013), Zhou et al. (2013), Wang et al. (2014) and O'Connor et al. (2014); and to Ornithurae by Gauthier (1986), Chiappe and Calvo (1994), Norell and Clarke (2001), Kurochkin et al. (2013), Wang et al. (2014) and Wang and Liu (2015).