The folk singer, born in Jacksonville, Florida, was best known for his worldwide 1967 hit single 'San Francisco (Be Sure to Wear Flowers in Your Hair)'.
The song became an anthem for the late 1960s counterculture and hippy movements, and has featured in a number of TV shows and films including Forrest Gump.
McKenzie's body was found by a neighbour at his home in Los Angeles, California on Sunday (August 19).
He had been suffering from the nervous system disease Guillain-Barre Syndrome.
"I think he had a heart attack this most recent time. He was in the hospital," neighbour Victoria Byers told BBC News. "They did not want him to leave the hospital, but he wanted to be in his house [when he died]."
After dropping out of the fame spotlight in the late 1960s, he re-emerged in the 1980s by joining close friend John Phillips in a new version of The Mamas and the Papas.
McKenzie also co-wrote The Beach Boys' hit single 'Kokomo'.
Watch Scott McKenzie perform 'San Francisco' below: