Another place name in Kerry: Dún Géagáin. Am I correct that Géagáin is a genitive? What is the correct form of the connected nominative? Would that be Géagan? Does anyone have more information about the Géagan who gave his name to this place?

Thanks in advance.

nominative: Géagán.
Acc. to https://www.logainm.ie/en/22069 nothing is known about the person himself.
-án is a diminutive ending meaning "little ..."
For the meanings of géag see here:
http://www.teanglann.ie/en/fgb/géag