Lieutenant-Colonel Sir Richard Henry Bonnycastle (30 September 1791 – 3 November 1847) was an officer of the British army active in Upper Canada.

He served at the siege of Flushing in 1809, and in the American campaigns of 1812–14, during which he was present at the capture of Fort Castine, and the occupation of the part of the state of Maine east of the Penobscot, and was commanding engineer at the construction of the extensive works thrown up by the British on the Castine peninsula.

[1] As commanding royal engineer in Upper Canada, he rendered very important services during the Canadian rebellion in 1837–39, particularly in February 1838, when, at the head of a force of militia and volunteers, in the absence of regular troops, he defeated the designs of the insurgents at Napanee, and the brigands at Hickory Island, for an attack on the city of Kingston.

[1] In his capacity as a military engineer, Bonnycastle oversaw the fortification of Fort Henry in modern Kingston, Ontario.

[1] Through his son, Henry William John Bonnycastle (1813–1888) would come a prominent Bonnycastle family of Canadian politicians and adventurers and the founder of Harlequin Enterprises, the world's largest publisher of romance novels.