HM Prison Armagh, also known as Armagh Gaol, is a former prison in Armagh, Northern Ireland. The construction of the prison began in 1780 to a design of Thomas Cooley and it was extended in the style of Pentonville Prison in the 1840 and 1850s. For most of its working life Armagh Gaol was the primary women's prison in Ulster. Although the prison is often described as Armagh Women's Gaol, at various points in its history, various wings in the prison were used to hold male prisoners.