Firth is a coastal island parish, which lies in Orkney Council Area, some 6 miles (10 km) northwest of Kirkwall and 8 miles (12 km) northeast of Stromness in Orkney.
It is located in the old county of Orkney, which disappeared following the Local Government (Scotland) Act 1974.
The parish has an area of 33.1 sq. km (12.8 sq. miles). Firth has 5 neighbouring parishes; namely Birsay & Harray, Evie & Rendall, Kirkwall & St Ola, Orphir and Stenness.