Jan, Looked up "McKinley" in the Scottish Clan and Family Names" book. It was spelled at one time "Mackinlay."
The clan country of the Mackinlays was the Lennox district, but records are obscure. The Mackinlays of Lennox descended from Findlay, a son of Buchanan of Drumikill. The other Lennox clans, many Mackinlays were also connected with Clan Farquharson, descendants of Farquharson of Braemar in the sixteenth century. There were Findlays or Mackinlays also in Lochalsh and Kintail. Variant spellings of Mackinlay are Donleavy, Finlay, Findlay, Finlayson, Macinally and Mackinley.
The name is also found in the North of Ireland among settlers of the Scots plantation of Ulster. William McKinley, 25th President of the US, was an Ulster Scot.