Gaius cooperi is a species of mygalomorph spider in the Idiopidae family. It is endemic to Australia. It was described in 2018 by Australian arachnologists Michael Rix, Robert Raven and Mark Harvey.[1]
The species occurs in south-west Western Australia in the Avon Wheatbelt, Esperance Plains, Jarrah Forest and Mallee bioregions. The type locality is Forrestania, some 400 km east of Perth.[1]