The police responded to a call about an unresponsive baby at Ewing's Love and Hope Preschool and Academy around 1 p.m. The baby was found on a car seat inside the van.
The co-owner of Ewing's Love and Hope Preschool and Academy, Darryl Ewing, 56, was arrested on Wednesday night for child neglect.
Jacksonville Sheriff's Chief Crimes Assistant Officer Chief Brian Kee told CNN that preliminary information shows he was in the van from 8 am until the call came.
Temperature in the area reached at 92 degrees high on Wednesday, according to CNN meteorologist Dave Hennen.
Kee said the day care facility used the van to pick up some children in the morning, and the day care worker is responsible for ensuring that all children are not in the van.
CNN called the facility. The person who replies is no comment.
The center cares about 14 children, and no one else is injured, Kee said.
Death investigation continues. There is no information on prison records when Ewing is in court or if he has a lawyer.