Shelby Carter, 21, apparently strapped her baby into a car seat, broke a second-floor window and dropped the child to the ground below, said Ed Foglesonger, chief of the volunteer fire department in Wyoming, Illinois.
"I guess it's the motherly instinct to take care of their young," he told CNN. "We're all wondering why she didn't go out after the baby."
Firefighters found Carter's body in a room on the second floor. An autopsy showed she died of smoke inhalation, the Peoria Journal Star reported
"The house was engulfed in flames," Stark County Sheriff Steve Sloan said in a statement. Carter "was a hero as she put her baby into a car seat and dropped the baby to the ground."
A woman called 911 on Monday morning and said she was inside a burning house and having trouble breathing, Foglesonger said. She didn't mention a baby, he said.
When firefighters arrived, they moved a pile of discarded carpet on the ground so they could climb a ladder to a second-floor window, he said. That caused a car seat to roll toward the house. They looked inside the car seat and found Keana Davis.
Firefighters rushed the baby to a nearby hospital. She was released and is now being cared for by relatives, Foglesonger said.
Carter and the baby lived in the house with her mother and fiancé, Foglesonger said, but only Carter and the baby were home when the fire broke out in the living room downstairs. The cause of the fire has not been determined.
The death was a gut punch for the town of about 1,500 people southwest of Chicago, where everybody seems to know each other.
For instance, Foglesonger said Carter's father works "works with me every day" at a company that makes boilers and water heaters.
"Words can not express the way we truly feel," the fire department said in a Facebook post.
Carter celebrated her birthday the day before her death. She graduated from the local high school in 2014, worked as a nail technician and was studying to become a pharmacy technician, her obituary said.
"She was making her mark in town," Mayor Pat Maher said. "She was very upbeat, always smiling."
A GoFundMe page
had raised more than $23,000 as of Friday evening to help the family.