Workmen clearing the wooded area, which is on private land, made the discovery.
Supt Eamonn Keogh, who is based at Baltinglass Garda station, said State Pathologist Marie Cassidy attended the scene yesterday and determined that the skull probably belonged to a man.
He said the best estimate was that the skull belonged to a male, aged between 18 and 50. He said the skull had probably been at the scene for between one and 20 years.
He said the skull had been removed from the scene for technical examination and there was unlikely to be any definite identification until later this evening or tomorrow.