Omosaurus armatus was named by Marsh (1877). Its type specimen is BMNH 46013, a set of postcrania, and it is a 3D body fossil. Its type locality is Swindon Brick and Tile Company brick pit, which is in a Kimmeridgian marine claystone in the Kimmeridge Clay Formation of the United Kingdom.

It was recombined as Stegosaurus armatus by Dollo (1889) and Gadow (1901); it was considered a nomen dubium by Maidment (2010); it was recombined as Dacentrurus armatus by Lucas (1902), Hennig (1915), Delair (1960), Delair (1973), Thulborn (1975), Galton (1982), Galton (1983), Galton (1985), Galton (1990), Galton (1991), Olshevsky and Ford (1993), Galton (1994), Casanovas-Cladellas et al. (1995), Casanovas-Cladellas et al. (1995), Sanz (2000), Pereda Suberbiola and Galton (2001), Carpenter et al. (2001), Blows (2001), Ruiz-Omeñaca and Canudo (2003), Pereda Suberbiola et al. (2003), Pereda Suberbiola et al. (2005), Mateus (2006), Escaso et al. (2006), Escaso et al. (2007), Maidment et al. (2008), Suñer et al. (2008), Naish and Martill (2008), García-Ramos et al. (2008), Cobos et al. (2008), Butler et al. (2008), Ortega et al. (2009), Pereda Suberbiola et al. (2009), Company et al. (2010), Mateus and Milàn (2010), Barrett and Maidment (2011), Gaete et al. (2011), Pascual et al. (2012), Cobos and Gascó (2013), Cobos et al. (2014), Ulansky (2014), Ulansky (2014), Saitta (2015), Borinder et al. (2016), Galton and Carpenter (2016), Costa and Mateus (2019), Mocho et al. (2019), Maidment et al. (2020) and Breeden et al. (2021).