The scared 4-year-old was found by people passing by a fenced-in area where the bus was parked on Chicago's South Side Friday.
After a few anxious hours his family was relieved to be reunited with 4-year-old Justin Gills.
For several hours earlier in the afternoon they had no idea where he was, and neither did he.
He woke up alone on a school bus and found himself locked inside this bus yard. His mother says she had no idea until paramedics called her to say her son was in the hospital.
"I asked to speak to Justin... Woke up and no one was there," said Latasha Burton.
After waking up on the bus, he managed to get out of the bus, but found he was still locked inside the parking lot. Several passersby heard his cries and stopped to help.
"The kid was crying, said he fell asleep on the bus and I guess when he woke up he couldn't get out of the wrought-iron gate and barb-wire fence," said William Reed.
"He was a little agitated," said Sheila Bradshaw. "He was disheveled because he didn't know who anybody (was). He was just a little bit upset and crying."
Justin's pre-school class had been on a field trip to a roller skating rink, but when the bus returned to let the other kids off at the school Justin remained on the bus, asleep.
The teachers and supervisors failed to notice he was not with the group and the bus driver also apparently failed to check the bus after parking in the yard.
ABC7 attempted to talk to officials at the bus company. They were in the office but refused to come to the door.
His mother says Justin is fine, but she has some concerns about how the school and bus company handled the situation.
"I need to know why wasn't a count done when the children were taken off the bus," Burton said. "Why didn't the driver check his bus?"
Several staff members at the school were unable to go on camera, but said nothing like this has ever happened before.
They were deeply concerned about Justin and greatly relieved he is safe tonight. His mother says she plans to talk further to school officials on Monday to try to get a better understanding of how this happened.