Grangegorman is located in the Dublin 7 postal district. North of the River Liffey and about 1 km from Dublin city centre, its boundaries run along Brunswick Street North, Prussia Street and Manor Street, the North Circular Road and Phibsborough Road and Constitution Hill. Grangegorman is surrounded to the south east by Smithfield to the west by Stoneybatter, north by Cabra, to the north and east by Phibsborough / Broadstone.
The geographical definition of the north Dublin electoral division known as Arran Quay B, encompasses Grangegorman. The 2006 Census gives the population of Arran Quay B as 3692. This represents a 19.5 per cent increase from the population of the area in 2002