Duncombe married, on 13 May 1841, Lady Harriet Christian Douglas,[6] the second child of Charles Douglas, 6th Marquess of Queensberry, and founder, in 1870, of York's St Stephen's Orphanage.[7] Lady Harriet died in London on 26 July 1902, at the age of 93.[8]
They had three daughters and two sons:
- Major Alfred Charles Duncombe, JP (1843–1925), who was High Sheriff of Staffordshire in 1883; married Lady Anne Florence Adelaide Montagu (d.1940), daughter of the 7th Earl of Sandwich; and died without issue.
- Major Adolphus Montagu Duncombe, JP (1852–1904), Yorkshire Hussars; married Beatrice Dorothy Mary Bridgeman-Simpson (d.1936), daughter of Rev. William Bridgman-Simpson by Lady Frances Laura Wentworth Fitzwilliam (who was a daughter of the 5th Earl FitzWilliam); and died without issue.