The location of the song seems to be The Barnesmore Gap, a major thoroughfare linking North and South Donegal. Barnesmore comes from the Irish "Bearnas Mór" meaning "Big Gap" The area was notorious for Rapparees, highwaymen and bandits in the distant past. The location of a gallows is still pointed out near the road.

The Finn is a river north of the gap. The Finn valley is the most fertile area in the district, so this is the land that would have been settled by the planters.

Ref:
https://en.wikipedia.org/wiki/Barnesmore_Gap

http://ballybofeyandstranorlar.com/barnesmore-gap/

http://www.askaboutireland.ie/reading-room/environment-geography/transport/infrastructure-in-county-/donegals-roads/

Sorry can't manage the Blue Link.