The boy was a passenger in a jeep, which collided with a van which was travelling in the same direction.
The driver and another passenger in the jeep were also taken to hospital. The driver of the van did not require hospital treatment.
The road is currently closed pending an examination by Garda Forensic Collision Investigators and diversions are in place.
Gardaí have appealed for witnesses to contact Mullingar Garda Station on 044-9384000, The Garda Confidential Telephone Line 1800 666 111, or any Garda Station.
