Hylaeosaurus was named by Mantell (1833). Its type is Hylaeosaurus oweni. It was considered monophyletic by Vickaryous et al. (2004).

It was assigned to Pachypodes by Meyer (1845); to Dinosauria by Quenstedt (1852); to Harpagosauria by Haeckel (1866); to Orthopoda by Cope (1866); to Dinosaurii by Quenstedt (1867); to Iguanodontidae by Cope (1870); to Dinosauria by Owen (1842), Owen (1858), Owen (1861) and Lydekker (1877); to Scelidosauridae by Huxley (1870), Marsh (1880), Sauvage (1882), Marsh (1884), Marsh (1885), Lydekker (1888), Lydekker (1888) and Marsh (1896); to Omosauridae by Huene (1909); to Stegosauridae by von Zittel (1911); to Acanthopholididae by Kuhn (1964); to Acanthopholidae by Nopcsa (1928), Stromer (1934), Romer (1956), Simmons (1965) and Romer (1966); to Nodosauridae by Coombs (1978), Coombs (1978), Molnar (1980), Sereno (1986), Tumanova (1987), Blows (1987), Carroll (1988), Pereda-Suberbiola (1993), Pereda Suberbiola and Galton (1997), Sereno (1998), Blows (1998) and Sereno (1999); to Polacanthinae by Pereda Suberbiola and Galton (2001); to Ankylosauria by Vickaryous et al. (2004); to Polacanthidae by Ford (2000), Carpenter (2001), Carpenter (2001) and Kilbourne and Carpenter (2005); and to Ankylosauria by Sachs and Hornung (2013).