Flag of the county of Caithness, Scotland

Caithness (/keɪθˈnɛs/; Scottish Gaelic: Gallaibh [ˈkal̪ˠɪv]; Old Norse: Katanes) is a historic county, registration county and lieutenancy area of Scotland. There are two towns, being Wick, which was the county town, and Thurso. The county includes the northernmost point of mainland Britain at Dunnet Head, and also the most north-easterly point at Duncansby Head near John o' Groats. The Flow Country is the largest blanket bog in Europe, and covers a large inland area in the west of the county. Caithness has a land boundary with the historic county of Sutherland to the west and is otherwise bounded by sea. The land boundary follows a watershed and is crossed by two roads (the A9 and the A836) and by one railway (the Far North Line). Across the Pentland Firth, ferries link Caithness with Orkney, and Caithness also has an airport at Wick. The Pentland Firth island of Stroma is within Caithness. From the 9th century the Caithness area was ruled by the Jarl of Orkney, who at different times owed allegiance to both Norway and Scotland. Caithness subsequently became a separate provincial lordship from Orkney in the 14th century, being an earldom controlled by the Earl of Caithness. The name was also used for the Diocese of Caithness from the 12th century to the 17th century. The diocese was larger than the later county, also including Sutherland. A shire called Caithness covering the same area as the earldom was created in 1641, after a couple of earlier abortive attempts. Shires gradually eclipsed the old provinces in administrative importance, and also became known as counties. The county ceased to be used for local government purposes in 1975, when the area became part of the Highland region, which in turn became a single-tier council area in 1996. There was a local government district called Caithness from 1975 to 1996, which was a lower-tier district within the Highland region. The pre-1975 county boundaries are still used for certain functions, being a registration county. The Norn language was historically the language of everyday communication for people in Caithness, but was gradually overtaken by Scots and then English. Norn had probably become extinct in Caithness by the 15th century.