Hilarius (floruit 408) was a politician of the Western Roman Empire.
Hilarius is known to be the praefectus urbi of Rome in 408.
He is attested in office on January 15 of that year by a law preserved in the Codex Theodosianus.
He has been sometimes identified with a Hilarius Praetorian prefect of Gaul in 396, but this identification is rejected by historians on the fact that the urban prefecture was a lesser office than the praetorian one.