Its county town is Peebles, and it borders Midlothian to the north, Selkirkshire to the east, Dumfriesshire to the south, and Lanarkshire to the west.

[1] The origins of Peeblesshire are obscure, but it became a shire sometime around the twelfth century, covering part of the historic district or province of Tweeddale.

The southern part of Tweeddale became the sheriffdom of Selkirkshire, also known as Ettrick Forest, whilst the northern part of Tweeddale was initially divided into two sheriffdoms, based at Peebles and Traquair, before those two were united as the single shire of Peebles, or Peeblesshire, around 1304.

[11] The coat of arms of the county, which was matriculated by the Lord Lyon in 1931, ia as follows: Quarterly, 1st sable five fraises (strawberry leaves) argent; 2nd azure, a horse's head couped argent; 3rd vert, a fleece or; 4th or, fretty gules, on a chief embattled of the last, two thunderbolts of the first.

The first quarter is the arms of Fraser of Oliver Castle, a prominent local laird; the second, that of Horsburgh, another prominent local laird; the third, a reference to the area's wool industry; and the fourth, that of M. G. (later Sir Michael) Thorburn of Glenormiston, who was sheriff of Peebles at the time of the arms' matriculation.