Joseph Hardcastle may refer to: Joseph Hardcastle (1752–1819), English merchant and a founder of The Missionary Society Joseph Hardcastle (politician), grandson of the above and British Liberal Party MP Joseph Alfred Hardcastle, FRAS (1868–1917), grandson of Joseph Hardcastle (politician) and Sir John Herschel appointed Director of Armagh Observatory just before his death Joseph Hardcastle (accountant) (died 1906), American Certified Public Accountant