In terms of area, the largest county in Ireland is county Cork at 7,457 km. The next largest is county Galway, at 6,148 km. The largest county in Northern Ireland is county Tyrone, at 3,155 km.Smallest county The smallest county in Ireland is county Louth, which is just 820 km in area - 9 times smaller than county Cork.The next smallest is county Carlow, which is 896 km.t is, in fact, the largest lake in the British Isles. Closest to Britain The closest point that Ireland comes to Britain is Torr Head, county Antrim, which is just 23 km (14 miles) from the Mull of Kintyre, Scotland. On most days, fields in Scotland can be seen clearly across the North Channel.