The baby's father, Antonio Francisco Balta, 27, was arrested and charged with aggravated manslaughter of a child. He was being held Sunday at the Broward County Jail without bail, the Miami Herald reported Monday.
The death happened Saturday at Gulfstream Park as crowds arrived to hear a concert and watch the Florida Derby, Hallandale Beach police said.
The child was left unattended in Balta's car, but they would not describe how the baby was left there, how long the baby was in the vehicle or what Balta was doing at the track.
Balta, while not employed by Gulfstream, worked as a groom for Nick Zito, a trainer whose horses race there.
The child's mother, Michelle Bashford, 22, was working as a waitress at the track's Royal Palm restaurant when the baby died.
Balta and Bashford were seasonal workers and, though married, have been separated for several years, family friends said.