Nithsdale (Scottish Gaelic: Srath Nid), also known as Strathnith, Stranith or Stranit, is the strath or dale of the River Nith in southern Scotland.

The provinces gradually lost their administrative importance to the shires created from the twelfth century, with Nithsdale forming part of Dumfriesshire.

Nithsdale was historically a strategically important area, lying on some of the main routes from England to the south into the rest of Scotland.

The province of Nithsdale bordered Annandale to the east, Clydesdale to the north, Kyle to the north-west and Galloway to the west.

Commissioners of Supply were created for each shire in 1667, and many of the old provinces (including Annandale and Eskdale) lost their hereditary rulers under the Heritable Jurisdictions (Scotland) Act 1746.

The district covered the western part of Dumfriesshire, and also included the parishes of Kirkbean, Kirkpatrick Irongray, New Abbey, Terregles, and Troqueer, which had formerly been in Kirkcudbrightshire.