Greencastle or Green Castle may refer to:
Places Germany Green Castle (Grünes Schloss), Weimar; see Duchess Anna Amalia Library
Ireland Greencastle, County Donegal, Republic of Ireland Greencastle, County Antrim, Northern Ireland, a townland and suburb of Belfast Greencastle, County Down, Northern Ireland Greencastle, County Tyrone, Northern Ireland
Scotland Green Castle, Portknockie, an Iron Age and Pictish promontory fort
United States Greencastle, Indiana, a city Greencastle, Missouri, a city Greencastle, Pennsylvania, a borough Greencastle, West Virginia, an unincorporated community Greencastle, Kanawha County, West Virginia, an unincorporated community
Other uses Greencastle (film)