Glencastle
Glencastle 
    Gleann Chaisil  | |
|---|---|
Townland  | |
Dún Domhnaill fort in Glencastle townland  | |
| Coordinates: 54°11′N 9°53′W / 54.183°N 9.883°W | |
| Country | Ireland | 
| Province | Connacht | 
| County | County Mayo | 
| Population  (2011)  | 38 | 
| (Glencastle townland only) | |
Glencastle (Irish: Gleann Chaisil) is a small village, electoral division and townland in the northwest of County Mayo, Ireland. The townland of Glencastle has an area of approximately 2,337 acres (9.46 km2).