The following is available (very nice) from a company which specializes in surname histories and scrolls.
MacKays first lived among the Pictish people of ancient Scotland. The name is derived from the personal name Aodh. The Gaelic form of the name is usually Mac Aoidh, and in Inverness, the Gaelic form of the name MacKay is Mac Ai. Among the founding tribes of Scotland, the Picts and the Dalriadans were two of the most powerful. They were united in 844 under the half-pictish, half-Dalriadans Kenneth MacAlpin. Because he held much of the country's territory, he is considered to have been Scotlands first true king.
Scotland saw its first hereditary surnames appear in the 11th and 12th centuries; this coincided with the widespread use of the clan system in Scotland. For purposes of identification and, in the case of the clan system, allegiance, patronymic names like MacKay were assumed. They took the name of the initial bearer's father and often added the prefix Mac, meaning "son of". Clan names work on the same principle, as clan is a patriarchal social group based around a symbolic father known as the chief.
During these years of development of names, spellings were by no means rigidly fixed. Repeated and inaccurate translation of Scottish names back and forth from Gaelic to English resulted in a wide variety of spelling variations of a Clan's name. MacKay has appeared McCaghe, McKuaye, McKuay, McCahe, Kaghe, Kaighe, McKaie, McCuay, McCaye, McKaghe, McCuaye, Kuaye, McKeighe, McQueye, McKaighe, Caghe, Queye, Cuaye, McQuey, and other ways in early documents.
The origins of ancient Scottish families are tracedtoday largely through such documents as the Exchequer Rolls of Scotland, the Inquisitio, the Ragman Rolls, the Domesday Book, clan genealogies, baptismals, parish records, cartularies, and tax records. The MacKay family originated in Moray, where the MacKay family resided in early times. Some experts theorize that they were part of the ancient Clann Morgunn.
Early records show that Gilcrest M'Ay, forefather of the MacKay family of Ugadale, made a payment to the constable of Tarbert in 1326. It is claimed that the clan is descended from the Royal hous of MacEth.
In 1415 the Lord of the Isles formally granted Angus, Chief of MacKay of Strathnaver, a large region of the northernmost tip of Scotland. Far removed from the Scottish throne, the clan subsequentely developed their power in relative isolation.
In 1539 King James 5 granted the clan the Barony of Farr. In the early 17th century, the clan made further gains in territories by participating in European campaigns, but they would soon lose much of their lands to their neighbors, the Sutherlands because of the bankcruptcy of Clan cheif, Lord Reay. The Sutherlands continued to acquire MacKay lands long after the Highland Clearances began.
There is also a branch of the MacKays much farther south; Robert the Bruce confirmed the Kintyre lands of Gilchrist Mac ymar McAy to the Clan in around 1329. The Lord of Islay granted a charter to a MacKay of Islay in 1408. The family was also established in Galloway.
Other records show RObert Makgye was royal jester to the king of Scotland between 1441 and 1450 and that Patrick McKe was burgess of Wigtown in 1575.
In the 17th century, the highland clans were seen as an anarchic force in the dominion of England.
The Scottish and English crowns had been united in 1603 and many families were forced to leave their northern homelands. An even greater exodus occured from the Highland Clearances of 1746 onward. Many ventured to the colonies of North America in search of freedom and opportunity. It was not long however, before the Scots in America were forced to stand up and defend their freedom, or join the British side in the American War of Independence. The ancestors of these Scots abroad have rediscovered their heritage in the last century through the clan societies and other organizations that have sprung up across North America.
Some of the family also moved to Ireland in the Plantation of Ulster. In 1890, a census of Scottish families in Ireland was taken. At that time it was estimated that there were over 268 people bearing the name Kee. All were found in the province of Ulster. The same census showed that there were over 1,702 people bearing the surname Mackey (about 26% in Ulster), over 2,867 had the surname McKay (about 87% in Ulster), and about 4,300 with the surname McKee (about 96% in Ulster).
The pattern of immigration to North America for the MacKays can be illustrated by a sample of early settlers; A MacKay from Kilkenny, Ireland settled at Bar Haven in the 17th century; a very large family of McKays arrived in Pennsylvania in 1772; George McKay landed at Wilmington with his wife and children in 1774, John McKay was a soldier in St. Johns in 1780; Edward Mackey landed in Chapels Cove in 1785; Mary MacKay landed in Brigus in 1801; and Thomas from Faha, Waterford, was married in Bonavista in 1803.
The 1984 edition of the Report of Distribution of Surnames in the Social Security lists McKay as the 791st most popular name in the United States. The same report lists McKee as the 663rd most popular.