The calculated distance (air line) between Maynooth and Dún Laoghaire is approximately 20 miles respectively 32 kilometers.
By car or train, the actual journey to Dún Laoghaire is certainly longer, as only the direct route (as the crow flies) between Maynooth and Dún Laoghaire has been calculated here.
Air line (approximately)
32 kilometers
17 nautical miles