The crash happened before 6:30 p.m. at the intersection of Ustick Road and Jullion Street.
According to witnesses, a car traveling west on Ustick collided with the girl who was crossing Ustick on her bike.
The Ada County Coroner's Office identified the girl as Olivia Schnacker of Boise. She died of blunt force trauma as a result of the crash and listed the death as an accident.
Witnesses say Schnacker was riding with two other kids when the crash happened, and that she was not wearing a helmet. Police say the female driver of the sedan is being cooperative.
The crash is still under investigation.
A memorial fund has been established at local Wells Fargo Banks. The account is listed under the "Olivia Schnacker Memorial Fund."