Cheshire Police said a man who was arrested as part of its investigation had since been released without charge.
After the baby, who has never been formally identified, was found in March 1998, local people arranged a burial and a funeral service was held.
The headstone, which was paid for with money raised by the community, bore an inscription dedicated to “Baby Callum, precious child of God”.
It added the child was “laid to rest July 27, 1998, with love, from the people of Warrington”.
