Where is area code 011?

011 is not an area code or a country code, it is the international access prefix used in North America (country code +1; USA, Canada, etc.). When you see a country code listed as, for example, +353, the plus sign means "insert your international access prefix here," so, from the US or Canada you would dial 011-353 for Ireland.

There are some countries in which 011 is a domestic area code; see the Related Questions below.