The passerby found the baby girl Tuesday evening, the Houston Chronicle said.
Officials said the baby was taken to Texas Children's Hospital and is in good condition.
The baby was naked but was clean, the Chronicle reported. The child's body temperature was said to be normal so she wasn't likely outside for long.
The woman said she found the baby after her dogs took an interest in a Walmart bag between a tree and a bush. The woman opened the bag and found the baby, the Chronicle said.
The incident is the third of its kind in Houston in a year, the Chronicle reported.
In September, a Houston woman was sentenced to two years probation and ordered to pay a $50 fine after she left her 3-year-old son at a bus stop, the Chronicle said.
And in the same month, a woman in her early 20's left a baby outside an urgent care clinic.