Comics and Graphic Novels cover all topics and can be found in every subject-based 'call-number' which start with a letter of the alphabet. Memoirs are shelved in the PN - PS section which are part of P:Language and Literature. History is shelved under D, E or F depending on which country the book covers. Q is where you will find the Sciences, R: Medicine, T: Technology, etc.
At the Interurban Library Comics and Graphic Novels can be found on the shelf next to Recreational Reading.
The Books and resources page walks you through search techniques for finding comics & graphic novels.