Roxburghshire is a Scottish border county. Its only low land lies in the North and in the larger river valleys. The southern portions are extremely hilly. The Cheviots mark the natural border with England. Peel Fell rises to 1,964 feet and Catcleuch Shin to 1,742 feet. The main mountains in Roxburghshire are Cauldleuch Head at 1,996 feet, Greatmoor rising to 1,964 feet, Din Fell rising to 1,735 feet, Arnton Fell at 1,464 feet, Windburgh at 1,622 feet, and Pennygant at 1,805 feet.
The shire is well watered. The River Tweed runs through the shire's north for twenty-six of its ninety-seven miles. Its tributaries are the Bowder and Teviot on the right bank, and the Eden and Allan on the left bank. The main river that is completely within the borders of the county is the Teviot River. It runs thirty-seven miles before it merges with the Tweed River. The main tributaries on the right bank are the Slitrig, the Allan Water, the Dean Vurn, the Jed, the Rule, the Oxnam, and the Kale, while the on the left bank are the Ale and the Borthwick Water.
In the south the main stream is the Liddel that runs for twenty-seven miles. Both the Liddel and the Kershope are borders with Cumberland in England. There are only a few smaller lakes in the county, namely the Primside Loch, Yetholm, and Horselaw. The main valleys are the Liddesdale, Teviotdale, Tweedside, and Jedvale.