The calculated distance (air line) between Ballincollig and Dún Laoghaire is approximately 142 miles respectively 228 kilometers.
By car or train, the actual journey to Dún Laoghaire is certainly longer, as only the direct route (as the crow flies) between Ballincollig and Dún Laoghaire has been calculated here.
Air line (approximately)
228 kilometers
123 nautical miles