The shooting happened around 10:42 p.m. Friday near San Lorenzo and E 1st streets, according to the Pomona Police Department.
Three victims were treated and released, and two others were listed in stable condition, police said in a statement.
One of the victims that was in critical condition passed away Saturday morning. The deceased was not immediately identified.
No arrest was announced and a description of a suspect was not released.
Details about what led up to the gunfire were not immediately available, but police said the party was primarily made up of college students and possibly some high school students.
Anyone with information about the shooting is urged to call the Pomona Police Department at (909) 620-2085. If you prefer to provide information anonymously, you may call Crime Stoppers at (800) 222-TIPS (8477).