In 1834, the library received a bequest from Thomas Telford, who was born at Glendinning and educated in Westerkirk. Telford was the greatest civil engineer of his day, responsible for a long list of building projects including roads, bridges, canals, aqueducts, harbours, fenland drainage, public buildings and churches. He never married, and in his will made bequests to a list of individuals, most of whom he had met and worked with during his career. To Langholm Library he left £1000, the capital to be invested and the interest used for buying books. In 1851, from the residue of his estate, a further sum of £2000 was added, the interest on this also to be used for buying books.
In 1853 Langholm Library absorbed the Langholm Trades Library (founded 1813). Since 1974, it has been a reference and local studies collection under the control of the Langholm Library Trust.
Today the collection consists of about 5,000 volumes including some items published in the eighteenth century and many books of local interest. There is also an important collection of books formerly belonging to Hugh MacDiarmid and bearing his autograph.