The name "Mackey" is pronunced with the stress on the first syllable. This is Irish, an Anglicized form of Gaelic Ó Macdha ‘descendant of Macdha’, a personal name meaning ‘virile’ or ‘manly’. With the stress on the second syllable, it is a variant of Scottish and Irish McKay.
 
The surname Mackey is derived from the Gaelic prefix "Mac", which means a male descendent of, and the anglicized form of the Gaelic "Aodh", meaning fire. Mackey family history shows many alternate spellings, including MacKey, McKee, McKay, McCay, and McCoy.
 
Mackey genealogy shows that the earliest recorded spelling of this name was made in 1098 and belongs to a Cucail Mac Aedha.

The History of the Mackey Family