Peeblesshire, also known as the County of Peebles or Tweeddale, was one of the 34 traditional counties into which Scotland was divided for administrative purposes. It was the most inland of the traditional county areas that today form Scottish Borders, and comprised the upper reaches of the valley of the River Tweed and the surrounding area. In one place it extended as far north as the spine of the Pentland Hills.
Peeblesshire was bordered to the west by the traditional county of Lanarkshire; to the north by West Lothian and Midlothian; to the south-east by Selkirkshire; and to the south by Dumfriesshire. Peeblesshire contained a small enclave of neighbouring Selkirkshire, (too small to show on the map) but this was given to Peeblesshire in a tidying up of the map of Scotland's counties which removed most enclaves and exclaves and reduced the total number of counties to 33 in 1890. Peeblesshire remained a county in its own right until reorganisation in 1975 swept all the counties away in favour of 12 regions.
The regions formed in 1975 were the upper tier of a two tier local authority system, and the area which had formed the traditional county of Peeblesshire became part of the region of Scottish Borders. Most regions were divided into a number of district council areas, and Scottish Borders had four of them. The area that had formed Peeblesshire became the district of Tweeddale.
Regions and districts disappeared from the scene in a major reorganisation in 1996, being replaced by 32 unitary council areas. What had started out as the traditional county of Peeblesshire is today the most north-westerly part of the unitary council area of Scottish Borders. For administrative purposes, Scottish Borders is divided into five area committee areas, which are partly based on the district council areas that preceded them. The Tweeddale area committee area inherited the boundaries of the Tweeddale District Council area.