A van carrying 19 people, all believed to be illegal immigrants, rolled early Friday on Interstate 80 in Cass County, the sheriff's office said.
The van was headed east when it rolled onto its side and ended up in the westbound lanes of traffic, officials said.
The accident happened just east of the U.S. Highway 71 interchange, near Atlantic in western Iowa.
Most of the people ran from the scene into a field. A baby and young child were among the van's passengers, the sheriff's office said.
When deputies found them, the children were being carried by their mother, Sheriff Bill Sage said.
Sixteen of the people were found over several hours of searching by deputies and volunteers from the Atlantic Fire Department.
The final three passengers were found about 6:30 a.m. about six miles southeast of the accident site, the sheriff's office said.
One woman was taken to a local hospital for minor injuries. Three others were taken to the hospital to be examined for exposure to the cold.
They were all released from the hospital and all 19 were turned over to immigration officials, Sage said.
He said the passengers indicated they were heading to New York. The van had California license plates, Sage said.