Hierosaurus coleii was named by Mehl (1936). Its type specimen is FHSM VP-14855 (= MU 650 VP), a partial skeleton, and it is a 3D body fossil. Its type locality is tributary of Smoky Hill River, which is in a Coniacian marine chalk in the Niobrara Formation of Kansas. It was considered monophyletic by Vickaryous et al. (2004).

It was recombined as Niobrarasaurus coleii by Carpenter et al. (1995), Ford (2000), Carpenter (2001), Ford and Kirkland (2001), Vickaryous et al. (2004), Carpenter and Everhart (2007), Osi and Makádi (2009), Loewen et al. (2013), Han et al. (2014), Galton (2019).