Horncastle is a town in Lincolnshire, England.
Horncastle may also refer to:
Places Horncastle (constituency), former constituency in Lincolnshire, England Horncastle, Berkshire, a suburb of Reading, England Horncastle, Ontario, Canada
People James Horncastle, writer John Horncastle, a bishop Tristan Horncastle, songwriter William Horncastle, cricketer
Other R v Horncastle UKSC 14, a decision of the UK Supreme Court
See also Louth and Horncastle (UK Parliament constituency)