From where did the name "McKinley" come?

Those of us in the family know that the family name should be Hoppenyan (or, perhaps, even Von Hoppen... I'm checking into that). Where did the McKinley name originate? Was it pulled out of a hat?

Lillian Maude McKinley (born 1881) married Maytor Hoppenyan (their son is the Maytor McKinley of Utter-McKinley fame). Eventually upon reaching California, Maytor Jr. decided to change his last name (for personal and business reasons) to McKinley. Eventually his siblings followed suit as well as his parents. So, his mother died with her maiden name (1950) as follows: Lillian Maude Hoppenyan McKinley.