Original: These counties are traditionally grouped into 4 provinces - Leinster (/O12/O), Munster (/O6/O) Connacht (/O5/O) and Ulster (/O9/O).
Simplified: The counties were in 4 provinces - Leinster (12 counties), Munster (/O6/O) Connacht (/O5/O) and Ulster (/O9/O).