Lieutenant-Colonel William Lambton, FRS (c. 1753 – 19 January 1823) was a British soldier, surveyor, and geographer.
Lambton was the Superintendent of the Trigonometrical Survey of India, which he began in 1802. He died and is buried at Hinganghat in Wardha district of Maharashtra. He was succeeded by his assistant George Everest.
Lambton was born at Crosby Grange, near Northallerton, in North Yorkshire, the son of a farmer. His skill in mathematics earned him a place in a grammar school and then, in 1781, an Ensignship in the 33rd Regiment of Foot. He was commissioned in the 33rd Regiment and his ability at surveying led to work on measuring land for settlers in America. He was appointed barrack master in Nova Scotia and he spent many years studying mathematics on his own. With his regiment he took part in the American War of Independence and was taken prisoner at Yorktown. After his release he was moved to New Brunswick and was involved in surveying the boundary between Canada and the United States. In 1795 the Duke of York ordered that all civilian officers should be struck off from the regiments. Lambton then joined the 33rd at Calcutta after 13 years away from regimental duties. The 33rd Regiment was commanded by Sir Arthur Wellesley at Calcutta.
In 1796 he was promoted to Lieutenant and posted with his regiment to India, under the leadership of Colonel Arthur Wellesley. He took part in the Fourth Anglo-Mysore War in 1799. After the capture of Mysore Lambton proposed that the territory be surveyed, using the new techniques of geodesy employed by William Roy in Great Britain, and this was approved. He began by measuring a base-line from St. Thomas Mount in Madras, from there proceeding by triangulation across the peninsula to Mangalore. His statue is placed in St. Thomas Mount. In 1806 he began his latitudinal measurement 100 miles northwards from Bangalore, where the British territory ended. He then surveyed southwards to Cape Comorin. Lambton then recommenced the survey northwards until his death. He was succeeded in the post by Valentine Blacker.
Lambton was made a Fellow of the Royal Society (9 January 1817) and a corresponding member of the French Academy of Sciences in 1817.