1 species has Rock Head as a hidden ability, 18 as a normal one

Effect, in PokéAPI's words

“Protects against recoil damage.”

As a hidden ability

Species	Slot	Note
Tyrantrum	Hidden

As a normal ability

Species	Slot	Note
Geodude	Normal
Graveler	Normal
Golem	Normal
Onix	Normal
Cubone	Normal
Marowak	Normal
Rhyhorn	Normal
Rhydon	Normal
Aerodactyl	Normal
Sudowoodo	Normal
Steelix	Normal
Aron	Normal
Lairon	Normal
Aggron	Normal
Relicanth	Normal
Bagon	Normal
Shelgon	Normal
Bonsly	Normal

Elsewhere in PokéAPI

5 more holders without a page here

Alternate forms and other species that PokéAPI lists with Rock Head.

Basculin Blue Striped, Marowak Alola (hidden), Marowak Totem (hidden), Growlithe Hisui (hidden), Arcanine Hisui (hidden)