Authorities say the female victim's body was discovered in a residential rear alley along the 7000 block of Greenwood Avenue, near Church Lane.
Paramedics were initially called to the scene around midnight Monday for a medical response.
They arrived to find the unidentified body in an alley area behind a row of twin homes, just steps away from a playground.
Police said the medical examiner determined the body is that of a white woman and ruled the death suspicious.
Additional testing will need to be done to determine the cause of death, but there was no evidence of blunt force trauma.
Investigators said they don't currently have any missing persons reported in Upper Darby.
Anyone with information is asked to call police.