Celebrity news website TMZ said he died after suffering a seizure at Chicago's Midway airport on Sunday morning.
The Cook County Medical Examiner's Office said the cause was unknown.
Juice Wrld, real name Jarad Anthony Higgins, was best-known for his viral 2018 hit Lucid Dreams. Mental health, mortality and drug use were common themes in his music.
His record label, Interscope Geffen A&M Records, said Juice Wrld was an "exceptional human being" who "made a profound impact on the world in such a short period of time".