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

It was assigned to Pachypodes by Meyer (1845); to Megalosaurinidae by d'Orbigny (1849); to Dinosauria by Owen (1842) and Quenstedt (1852); to Dinosauria by Pictet (1853); to Deinosauria by Mantell (1854); to Orthopoda by Cope (1866); to Harpagosauria by Haeckel (1866); to Dinosaurii by Quenstedt (1867); to Iguanodontidae by Gervais (1859) and Cope (1869); to Dinosauria by Owen (1854), Owen (1858), Owen (1859), Owen (1860), Owen (1861) and Lydekker (1877); to Stegosauria by Quenstedt (1882); to Stegosauria by Dollo (1889); to Scelidosauridae by Huxley (1870), Marsh (1880), Sauvage (1882), Dollo (1884), Marsh (1884), Marsh (1885), Lydekker (1888), Lydekker (1888), Zittel (1890) and Marsh (1896); to Stegosauri by Gadow (1901); to Omosauridae by Huene (1909); to Stegosauridae by Nopcsa (1901), von Zittel (1911) and Hennig (1915); to Acanthopholinae by Nopcsa (1929) and Nopcsa (1931); to Acanthopholidae by Nopcsa (1923), Nopcsa (1928), Nopcsa (1928), Stromer (1934), Romer (1956), Tatarinov (1964), Simmons (1965) and Romer (1966); to Acanthopholididae by Kuhn (1964) and Charig (1967); to Ornithischia by Gardiner (1982); to Polacanthiidae by Naish and Martill (2001); to Ankylosauria by Vickaryous et al. (2004); to Polacanthidae by Ford (2000), Carpenter (2001), Carpenter (2001) and Kilbourne and Carpenter (2005); to Polacanthinae by Pereda Suberbiola and Galton (2001), Kirkland and Loewen (2011) and Kirkland et al. (2013); to Ankylosauria by Coombs (1979), Benton et al. (2000) and Sachs and Hornung (2013); and to Nodosauridae by Coombs (1978), Coombs (1978), Molnar (1980), Sereno (1986), Tumanova (1987), Blows (1987), Carroll (1988), Pereda-Suberbiola (1993), Norman (1997), Pereda Suberbiola and Galton (1997), Sereno (1998), Knoll et al. (1998), Blows (1998), Sereno (1999), Barrett and Maidment (2011), Han et al. (2014), Blows and Honeysett (2014) and Yang et al. (2017).