Authorities said a volunteer discovered the baby's body in a garbage bag Monday afternoon.
The body was taken to Sioux City, Iowa, for an autopsy.
No charges have been filed against the mother.
Authorities believe the baby was born in Union county on Feb. 2 and placed in trash that was taken to the landfill near Jackson, Neb.
Crews have been searching for three weeks and had planned to call off the search on Thursday.