Namesakes
Irish Kings:
3 kings
King Diarmait mac Cerbaill (a.k.a. Diarmaid) 545-565 
King Diarmait mac Áeda Sláine (a.k.a. Diarmaid) 658-665
King Diarmait mac Máel na mBó (a.k.a. Diarmaid) 1042-1072
Saints:
2 blessed
Blessed Diarmaid ?-851
Blessed Dermot O'Hurley (a.k.a. Diarmaid) 1519-1584