The little girl was discovered by a worker sorting refuse at the Greenstar plant in Bray, which takes waste from across the country.
The infant was naked, but apparently uninjured, and a post-mortem will be needed later to reveal the cause of death.
Detectives investigating the case say they're concerned for the child's mother who they have promised to treat sensitively.
A dedicated helpline has been established by the Child and Family Agency, Tusla.
Tusla says the phone line will be manned by experienced professional staff who will provide all support necessary should the mother call.
The helpline number is 076 695 8400.
