Three robberies were reported at the end of September in the Washington Park neighborhood on the South Side.
In the incidents, at least one person approached the victims on the street or in a parking lot and showed a weapon, Chicago Police said.
The most recent happened about 12:15 a.m. Saturday in the 100 block of West Garfield Boulevard, police said. Another robbery happened in the same block about 4:10 a.m. Sept. 27.
An earlier robbery happened between 3:30 and 4 p.m. Sept. 20 in the 5500 block of South Wentworth, police said.
Anyone with information was asked to call Area Central detectives at (312) 747-8380.