Police have not release many details. But they did say the 25-year-old man was being detained in the city's Lawndale neighborhood in connection with a robbery.
Officers responded around 8:10 p.m. Monday to the 1600-block of South Pulaski Road. During the robbery investigation, the man became unresponsive.
Paramedics were called to the scene for a "person down from unknown causes," Chicago Fire Department Commander Curtis Hudson said. The man was transported to Mount Sinai Hospital, where he was pronounced dead. His identity has not yet been released.
Area Central detectives are conducting a death investigation.
The Sun-Times Media Wire contributed to this report.