Leath was one of the wards of the historic county of Cumberland in north west England.
In the Imperial Gazetteer of England and Wales (1870–72) John Marius Wilson described Leath: LEATH, a ward in Cumberland; bounded by Northumberland, Durham, and Westmoreland, and by the wards of Eskdale and Allerdale; and containing Addingham parish, twenty other parishes, and part of another.
Market towns in the ward were Penrith (the largest settlement and seat of local government), Kirkoswald and Alston.
A large part of the ward once made up the main part of the Royal hunting ground known as Inglewood Forest, which was subject to Forest Laws up until the reign of Henry VIII.
The manors of Penrith, Langwathby, Castle Sowerby and Great Salkeld and at times Glassonby and Gamblesby were part of the royal estate known as the Honour of Penrith, which eventually passed into the hands of the Dukes of Devonshire.