The name ` Hornsby ' comes from a convict who became a constable . His name was Samuel Henry Horne , and he was given some land for helping catch two bushrangers , whose names were Dalton and MacNamara . The name Hornsby is derived from Convict-turned-Constable Samuel Henry Horne , who took part in the apprehension of bushrangers Dalton and MacNamara on June 22 , 1830 .