Knockfin is bounded on the west by Curraghnabania and Seltanahunshin townlands and on the east by Corraleehanbeg, Garryfliugh and Prabagh townlands. Its chief geographical features are Sliabh an Iarainn mountain on whose eastern slope it lies, mountain streams, waterfalls, a lime-kiln and dug wells. It is traversed by minor public roads and rural lanes. The townland covers 228 statute acres.