Within the text of the play, Macduff is Thane of Fife in Scotland which puts him on an equal playing field with Macbeth before Macbeth is awarded another "Thaneship" having overthrown Macdonwald.
Historically, the character of Macduff did not exist although Macbeth and Banquo did. The play was written for James I of England who had Scottish ties and was supposedly descended from the long line of kings prophesied by the witches from Banquo's issue.
The Macduff Clan, however, was a very powerful family in the middle ages in Fife. The remains of their castle can still be visited today.