Sarah Navas Sallas, 6, was last seen in the area of the 4400-block of South Albany Avenue at about 11:59 p.m. on Saturday.
Sarah is three feet tall, 38 pounds with brown eyes and brown shoulder-length hair. Police said she was last seen wearing a unicorn print white and pink sweater, blue jeans and glasses.
The girl is believed to be with her grandmother, Nexy Castillo-Gonzales.
Castillo-Gonzalez is 46 years old, five feet, four inches tall, 150 pounds with brown eyes and maroon hair. She was last seen wearing a gray shirt with white stripes, blue jeans, purple jacket and gray boots.
Anyone with information is asked to contact Area One detectives at (312) 747-8380.