The girl, Julia, disappeared with her dog from the village of Pierzwin in western Poland on Friday, RIA Novosti reported.
More than 250 firefighters, police officers, rescue workers and local residents searched for the girl throughout the night, Vesti FM radio reported. She was found Saturday, lying in nearby marshland with the dog by her side.
Firefighters who found Julia said the dog kept her warm enough through the night, when temperatures got down to 23 degrees.
Julia was taken to a local hospital because she appeared to have suffered some frostbite, hospital workers said. Her condition is not life-threatening.