Tiercahan is bounded on the north by Gortlaunaght townland, on the west by Borim (Kinawley), Gorteen (Kinawley), Gortnaleg, and Killaghaduff townlands and on the east by Drumbar (Kinawley) and Newtown (Kinawley) townlands.
Its chief geographical features are the Blackwater river which later flows into the River Cladagh (Swanlinbar), mountain streams, woods, a pool, water sink-holes, spring wells and a gravel pit. Tiercahan is traversed by minor public roads and rural lanes. The townland covers 173 statute acres.
Tiercahan National School, Roll No. 7,769, was not actually in Tiercahan townland. It was situated first in Drumbar (Kinawley) townland and later in Cullion (Kinawley) townland.
In the 1821 Census of Ireland there were twenty-two households listed in the townland.
In the 1901 census of Ireland, there were ten families listed in the townland.
In the 1911 census of Ireland, there were six families listed in the townland.