Banana Sam was located Saturday night in Stern Grove Park, said authorities.
Officials said that a park visitor noticed the 17-year-old monkey and lured him into his backpack. That visitor alerted police, who retrieved Banana Sam.
The primate was returned to the zoo in good health.
His theft Thursday prompted the zoo to boost security and keep the other 17 squirrel monkeys indoors.
Banana Sam was taken after thieves cut through a gate and made holes in the mesh surrounding the monkey exhibit.
The Associated Press contributed to this report.