Glennon is an American given name of Scottish origin, meaning 'fair-haired'. It is traditionally a boy's name but can also be used for girls. The name was popularized in the United States during the 1960s and 1970s.
"The name Glennon peaked in popularity between the early 1920s and late 1940s, with a significant decline from the mid-1950s onwards, becoming quite rare after the 1960s."