one , ▁F erman agh ▁and ▁a ▁southern ▁part ▁of ▁London der ry ▁( in ▁present - day ▁Northern ▁Ireland ). ▁According ▁to ▁ ▁Geoff rey ▁Ke ating , ▁it ▁included ▁the ▁baron ies ▁of ▁Car bury ▁( , ▁in ▁County ▁S lig o ), ▁Ros c log her ▁( , ▁in ▁County ▁Le it rim ), ▁and ▁Mag her ab oy ▁( , ▁mainly ▁To or ah ▁or ▁Tu ath ▁R ath a ) ▁and ▁F irl urg ▁( , ▁in ▁County ▁F erman agh ). ▁As ▁such ▁it ▁had ▁a ▁size ▁varying ▁between ▁that ▁of ▁C ors ica ▁( 8 , 6 8 0   km 2 ) ▁and ▁Leb anon ▁( 1 0 , 4 5 2   km 2 ). ▁ ▁Associ ated ▁arist ocracy ▁Although ▁the ▁elect ive ▁Ch ie ft ain cy ▁of ▁O ' D onn ell ▁is ▁ext inct ▁since ▁the ▁abol ition ▁of ▁Tan istry ▁and ▁Bre hon ▁Law , ▁the ▁Chief ▁of ▁the ▁Name ▁is ▁known ▁as ▁The ▁O ' D onn ell ▁of ▁T yr conn ell , ▁as ▁recogn ised ▁by ▁the ▁Chief ▁Her ald ▁of ▁Ireland , ▁as ▁the ▁legit imate ▁successor ▁in ▁a ▁put ative ▁sequence ▁of ▁Chief s ▁of ▁the ▁Name ▁( by ▁male ▁prim ogen iture ), ▁and ▁would ▁default ▁to ▁the ▁Duke ▁of ▁T et uan ▁in ▁Spain ▁in ▁succession ▁to ▁the ▁current ▁Chief , ▁a ▁Francis can ▁priest , ▁who ▁has ▁no ▁el ig ible ▁pro gen y . ▁However , ▁following ▁advice ▁by ▁the