Lieutenant-Colonel John By (7 August 1779 – 1 February 1836) was a British military engineer, best remembered for supervising the construction of the Rideau Canal and, in the process, founding what would become the city of Ottawa. Born in Lambeth in London, England in 1779 to George By and Mary Bryan. By studied at the Royal Military Academy. He was commissioned in the Royal Artillery on 1 August 1799 but transferred to the Royal Engineers on 20 December the same year. In 1802 he was posted to Canada for the first time, where he worked on the fortification of Quebec City and on improving the navigability of the Saint Lawrence River. During the Napoleonic wars he returned to Europe, where he served in Spain under the Duke of Wellington from 1811 until 1815.
With the end of the war By retired from the military but in 1826, in view of his engineering experience in Canada, he was recalled and returned to Canada to supervise the construction of the Rideau Canal. Since the canal was to begin in the wild and sparsely populated Ottawa River valley, his first task was the construction of a town to house the men who were to work on the canal, and associated services. The resulting settlement, called Bytown in his honour, would later become famous under the new name of Ottawa.
The canal was completed in six years, and was acclaimed as an engineering triumph. Colonel By was recalled to London, however, to face accusations that he had made a number of unauthorised expenditures. The charges were spurious and a parliamentary committee exonerated him, but the damage was done and he was never given a formal commendation for his work on the canal. He died in 1836 and is buried in the village of Frant in East Sussex in the South East of England.