IMO

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Note added at 7 mins (2006-05-30 06:48:45 GMT)
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The following text may be helpful to you.
QUOTE:
Thomas GILLILAND was born 1737. He died 1800 in Wilkes Co, GA. Thomas married Ann.

From Bruce Gilliland ([email protected]), April 19, 2000:
"Surnames of Scotland" by George F. Black states that Gilliland and Gillilan are derived from the Gaelic MacGill'Fhaoláin which means "son of the servant of (S.) Fillan."

The Historical Research Center, a commercial "heraldic" business states that

"The Irish surname Gilliland is an Anglicization of the Gaelic Mac Giolla Fhaolain. The Mac Giolla Fhaolain was a sept [A division of a family, especially a division of a clan ] of the Ui Fiachrach and held their lands in the region of County Sligo. In modern times, however, Gilliland is most numerous in the northern counties of Derry and Antrim. This suggests that many modern bearers of this surname may trace their origins to the Scottish settlers who came to Ulster in the sixteenth and seventeenth centuries. There was a Scottish clan called Mac Gill'Fhaolain (son of the servant of Fillan) and this Scots Gaelic surname was also anglicized 'Gilliland'."

In the 1600s, a number of Scottish families emigrated to Ireland as part of England's efforts to control Ireland. They became the "Scots-Irish" we often hear about. By the 1700's economic restrictions by England and political unrest in Ireland caused many families to come to America.

There are a number of documented Gilliland families coming from Ireland, but I have also seen references of Gillilands from Scotland as well.
In all likelihood, Gillilands (and other derivative spellings) are from Ireland or Scotland. Many Scots settled in Ireland along with British (much to the dislike of the Irish) before their descendants came to America.
END QUOTE:
http://wehaveneatstuff.com/williamsc/aqwg35.htm

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Note added at 14 mins (2006-05-30 06:55:28 GMT)
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So, according to the source, the original Scottish spelling of the name is "Mac Gill'Fhaolain".

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Note added at 49 mins (2006-05-30 07:31:17 GMT)
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Please also see this link.
http://www.thegillilands.org/history.php

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Note added at 2 hrs (2006-05-30 08:50:02 GMT)
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Gilliland

The name Gilliland in Ireland is derived from the native Gaelic Mac Giolla Fhaolain Sept of County Sligo although the name is now mostly found in Ulster Province. This Sept name was also anglicized as MacLellan. The name was also brought to the country by settlers who arrived into Ulster, especially during the seventeenth century.
http://www.irishsurnames.com/cgi-bin/gallery.pl?name=gillila... capname=Gilliland&letter=g&user=iis

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Note added at 2 hrs (2006-05-30 08:51:01 GMT)
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http://www.irishsurnames.com/cgi-bin/gallery.pl?name=gillila...