Cognomen Birkir (Birkir 
) , in the world, is an extremely rare surname. Much more frequently, Birkir is the forename as well as the last name.
Svan, Reynisson, Gretarsson, Larusson, Traustason, Einarsson, Ólafsson, Marteinsson, Sigurðsson, Stefánsson, Baldvinsson, Pétursson, Guðmundsson, Halldórsson, Hafsteinsson, Hjartarson, Sveinbjoernsson, Kristinsson, Ragnarsson, Gunnarsson, Ingibergsson, Sigurðarson, Karlsson, Benediktsson, Björnsson, Baldursson, Örn, Arson, Blær, Kúld, Rnason, Rnsson, Freyr, Gudnason, Fannar, Þrastarson, Skúlason, Brimdal, Karason, Jonsson, Jónsson, Helgason, Hreinsson, Árnason, Sveinsson, Arnaldsson, Arnarsson, Bjornsson, and Kristjánsson