First responders took the baby to a nearby hospital, where doctors said she appeared to be "doing okay," police tweeted.
Now, investigators are trying to track down the infant's mother.
"WE NEED HELP locating the parents to get them the assistance that they need," the department tweeted. "Mom, if you're reading this, call us."
Police added that they are "receiving an influx of calls requesting information on how to adopt the baby."
"While we appreciate the outpouring of support, the UDPD is not involved in this process," the department tweeted. "Please only call with pertinent information that may identify the family of the child."
Anyone with information about the parents' identities should call 610-734-7693 or email firstname.lastname@example.org.