Mackinley is a spelling variant of McKinley, a Scottish and Irish surname meaning son of the fair warrior.
Mackinley is an elaborated feminine or gender-neutral variant of McKinley, a Scottish and Irish surname meaning 'son of Finlay' — with Finlay itself derived from the Old Norse Finnlæikr, meaning 'fair hero' or 'fair warrior.' The Mac- prefix signals Scottish Gaelic descent, and the name was common enough in the Highlands that it spread with Scots-Irish immigration to North America, where it became a settled surname in the colonial period.
As a given name, McKinley has long carried an American presidential association: William McKinley, the 25th President, was assassinated in 1901, and his name was given to the highest peak in North America — now officially Denali, but still widely called Mount McKinley in everyday speech. The Mackinley spelling feminizes the name somewhat, softening the hard Mac- with a slightly more elaborate orthography, and it participates in the broader American trend of converting presidential and geographical surnames into given names — a tradition that has produced Lincoln, Monroe, Madison, Kennedy, and Reagan as popular given names across genders. Mackinley sits at the confluence of several naming currents: the prestige of -ley endings, the frontier romance of mountain geography, and the American habit of wearing history lightly by borrowing a famous surname and redeploying it as something personal and fresh. For a child named Mackinley, the name carries altitude — both literally, in its association with North America's highest summit, and figuratively, in the aspiration encoded in 'fair hero' buried in its ancient Gaelic root.