An FBI spokesman said Kayden Powell, of Beloit, was found in a bassinet at a truck stop near West Branch by a local police chief after he heard the baby's cries, the Janesville (Wis.) Gazette reported.
Kayden was found near where his aunt was taken into custody on a Texas fraud warrant, the FBI spokesman said.
The spokesman said the baby was doing "very well," calling the infant "amazingly resilient."
Officials had said she had left Beloit early Thursday about the time the baby was last seen.
No charges had been filed as of early Friday. Rock County Sheriff Bob Spoden said the county attorney and the U.S. Attorney's Office in Iowa would meet to decide "what charges are possible."