Colton police officers responded to Linko's Bar in the 100 block of E. Valley Boulevard around 1:40 a.m. Sunday.
When officers arrived, they found a 31-year-old woman shot in the upper body. She later died at a nearby hospital.
Investigators said it appears the victim was shot inside the establishment, but the circumstances surrounding the shooting are still being investigated.
No suspect description was immediately available. Anyone with information on the incident is asked to contact the Colton Police Department Detective Bureau at (909) 370-5000.