Wigtownshire or the County of Wigtown (Scottish Gaelic: Siorrachd Bhaile na h-Ùige, Scots: Wigtounshire) is one of the historic counties of Scotland, covering an area in the south-west of the country. Until 1975, Wigtownshire was an administrative county used for local government. Since 1975 the area has formed part of Dumfries and Galloway for local government purposes. Wigtownshire continues to be used as a territory for land registration, being a registration county. The historic county is all within the slightly larger Wigtown Area, which is one of the lieutenancy areas of Scotland and was used in local government as the Wigtown District from 1975 to 1996.

Wigtownshire forms the western part of the medieval lordship of Galloway, which retained a degree of autonomy until it was fully absorbed by Scotland in the 13th century. In 1369, the part of Galloway east of the River Cree was placed under the control of a steward and so became known as the Stewartry of Kirkcudbright. The rest of Galloway remained under the authority of a sheriff, and became known as the Shire of Wigtown, or Wigtownshire. The area was also sometimes called West Galloway (Scottish Gaelic: Gallobha-an-iar). The county town was historically Wigtown, with the administrative centre moving to Stranraer, the largest town, following the creation of Wigtownshire County Council in 1890.